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| # Question Description | ||
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| <p>Given an array of integers <code>nums</code> and an integer <code>target</code>, return <em>indices of the two numbers such that they add up to <code>target</code></em>.</p> | ||
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| <p>You may assume that each input would have <strong><em>exactly</em> one solution</strong>, and you may not use the <em>same</em> element twice.</p> | ||
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| <p>You can return the answer in any order.</p> | ||
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| <p> </p> | ||
| <p><strong>Example 1:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> nums = [2,7,11,15], target = 9 | ||
| <strong>Output:</strong> [0,1] | ||
| <strong>Explanation:</strong> Because nums[0] + nums[1] == 9, we return [0, 1]. | ||
| </pre> | ||
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| <p><strong>Example 2:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> nums = [3,2,4], target = 6 | ||
| <strong>Output:</strong> [1,2] | ||
| </pre> | ||
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| <p><strong>Example 3:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> nums = [3,3], target = 6 | ||
| <strong>Output:</strong> [0,1] | ||
| </pre> | ||
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| <p> </p> | ||
| <p><strong>Constraints:</strong></p> | ||
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| <ul> | ||
| <li><code>2 <= nums.length <= 10<sup>4</sup></code></li> | ||
| <li><code>-10<sup>9</sup> <= nums[i] <= 10<sup>9</sup></code></li> | ||
| <li><code>-10<sup>9</sup> <= target <= 10<sup>9</sup></code></li> | ||
| <li><strong>Only one valid answer exists.</strong></li> | ||
| </ul> | ||
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| <p> </p> | ||
| <strong>Follow-up: </strong>Can you come up with an algorithm that is less than <code>O(n<sup>2</sup>) </code>time complexity? |
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| # Question Description | ||
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| <p>You are given two <strong>non-empty</strong> linked lists representing two non-negative integers. The digits are stored in <strong>reverse order</strong>, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list.</p> | ||
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| <p>You may assume the two numbers do not contain any leading zero, except the number 0 itself.</p> | ||
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| <p> </p> | ||
| <p><strong>Example 1:</strong></p> | ||
| <img alt="" src="addtwonumber1.jpg" style="width: 483px; height: 342px;" /> | ||
| <pre> | ||
| <strong>Input:</strong> l1 = [2,4,3], l2 = [5,6,4] | ||
| <strong>Output:</strong> [7,0,8] | ||
| <strong>Explanation:</strong> 342 + 465 = 807. | ||
| </pre> | ||
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| <p><strong>Example 2:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> l1 = [0], l2 = [0] | ||
| <strong>Output:</strong> [0] | ||
| </pre> | ||
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| <p><strong>Example 3:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> l1 = [9,9,9,9,9,9,9], l2 = [9,9,9,9] | ||
| <strong>Output:</strong> [8,9,9,9,0,0,0,1] | ||
| </pre> | ||
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| <p> </p> | ||
| <p><strong>Constraints:</strong></p> | ||
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| <ul> | ||
| <li>The number of nodes in each linked list is in the range <code>[1, 100]</code>.</li> | ||
| <li><code>0 <= Node.val <= 9</code></li> | ||
| <li>It is guaranteed that the list represents a number that does not have leading zeros.</li> | ||
| </ul> |
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Notes/Questions/0003__longest-substring-without-repeating-characters/readme.md
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| # Question Description | ||
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| <p>Given a string <code>s</code>, find the length of the <strong>longest substring</strong> without repeating characters.</p> | ||
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| <p> </p> | ||
| <p><strong>Example 1:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = "abcabcbb" | ||
| <strong>Output:</strong> 3 | ||
| <strong>Explanation:</strong> The answer is "abc", with the length of 3. | ||
| </pre> | ||
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| <p><strong>Example 2:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = "bbbbb" | ||
| <strong>Output:</strong> 1 | ||
| <strong>Explanation:</strong> The answer is "b", with the length of 1. | ||
| </pre> | ||
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| <p><strong>Example 3:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = "pwwkew" | ||
| <strong>Output:</strong> 3 | ||
| <strong>Explanation:</strong> The answer is "wke", with the length of 3. | ||
| Notice that the answer must be a substring, "pwke" is a subsequence and not a substring. | ||
| </pre> | ||
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| <p> </p> | ||
| <p><strong>Constraints:</strong></p> | ||
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| <ul> | ||
| <li><code>0 <= s.length <= 5 * 10<sup>4</sup></code></li> | ||
| <li><code>s</code> consists of English letters, digits, symbols and spaces.</li> | ||
| </ul> |
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Notes/Questions/0004__median-of-two-sorted-arrays/readme.md
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| # Question Description | ||
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| <p>Given two sorted arrays <code>nums1</code> and <code>nums2</code> of size <code>m</code> and <code>n</code> respectively, return <strong>the median</strong> of the two sorted arrays.</p> | ||
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| <p>The overall run time complexity should be <code>O(log (m+n))</code>.</p> | ||
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| <p> </p> | ||
| <p><strong>Example 1:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> nums1 = [1,3], nums2 = [2] | ||
| <strong>Output:</strong> 2.00000 | ||
| <strong>Explanation:</strong> merged array = [1,2,3] and median is 2. | ||
| </pre> | ||
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| <p><strong>Example 2:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> nums1 = [1,2], nums2 = [3,4] | ||
| <strong>Output:</strong> 2.50000 | ||
| <strong>Explanation:</strong> merged array = [1,2,3,4] and median is (2 + 3) / 2 = 2.5. | ||
| </pre> | ||
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| <p> </p> | ||
| <p><strong>Constraints:</strong></p> | ||
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| <ul> | ||
| <li><code>nums1.length == m</code></li> | ||
| <li><code>nums2.length == n</code></li> | ||
| <li><code>0 <= m <= 1000</code></li> | ||
| <li><code>0 <= n <= 1000</code></li> | ||
| <li><code>1 <= m + n <= 2000</code></li> | ||
| <li><code>-10<sup>6</sup> <= nums1[i], nums2[i] <= 10<sup>6</sup></code></li> | ||
| </ul> |
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Notes/Questions/0005__longest-palindromic-substring/readme.md
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| # Question Description | ||
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| <p>Given a string <code>s</code>, return <em>the longest palindromic substring</em> in <code>s</code>.</p> | ||
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| <p> </p> | ||
| <p><strong>Example 1:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = "babad" | ||
| <strong>Output:</strong> "bab" | ||
| <strong>Explanation:</strong> "aba" is also a valid answer. | ||
| </pre> | ||
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| <p><strong>Example 2:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = "cbbd" | ||
| <strong>Output:</strong> "bb" | ||
| </pre> | ||
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| <p> </p> | ||
| <p><strong>Constraints:</strong></p> | ||
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| <ul> | ||
| <li><code>1 <= s.length <= 1000</code></li> | ||
| <li><code>s</code> consist of only digits and English letters.</li> | ||
| </ul> |
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| # Question Description | ||
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| <p>The string <code>"PAYPALISHIRING"</code> is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)</p> | ||
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| <pre> | ||
| P A H N | ||
| A P L S I I G | ||
| Y I R | ||
| </pre> | ||
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| <p>And then read line by line: <code>"PAHNAPLSIIGYIR"</code></p> | ||
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| <p>Write the code that will take a string and make this conversion given a number of rows:</p> | ||
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| <pre> | ||
| string convert(string s, int numRows); | ||
| </pre> | ||
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| <p> </p> | ||
| <p><strong>Example 1:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = "PAYPALISHIRING", numRows = 3 | ||
| <strong>Output:</strong> "PAHNAPLSIIGYIR" | ||
| </pre> | ||
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| <p><strong>Example 2:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = "PAYPALISHIRING", numRows = 4 | ||
| <strong>Output:</strong> "PINALSIGYAHRPI" | ||
| <strong>Explanation:</strong> | ||
| P I N | ||
| A L S I G | ||
| Y A H R | ||
| P I | ||
| </pre> | ||
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| <p><strong>Example 3:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = "A", numRows = 1 | ||
| <strong>Output:</strong> "A" | ||
| </pre> | ||
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| <p> </p> | ||
| <p><strong>Constraints:</strong></p> | ||
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| <ul> | ||
| <li><code>1 <= s.length <= 1000</code></li> | ||
| <li><code>s</code> consists of English letters (lower-case and upper-case), <code>','</code> and <code>'.'</code>.</li> | ||
| <li><code>1 <= numRows <= 1000</code></li> | ||
| </ul> |
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| # Question Description | ||
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| <p>Given a signed 32-bit integer <code>x</code>, return <code>x</code><em> with its digits reversed</em>. If reversing <code>x</code> causes the value to go outside the signed 32-bit integer range <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>, then return <code>0</code>.</p> | ||
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| <p><strong>Assume the environment does not allow you to store 64-bit integers (signed or unsigned).</strong></p> | ||
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| <p> </p> | ||
| <p><strong>Example 1:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> x = 123 | ||
| <strong>Output:</strong> 321 | ||
| </pre> | ||
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| <p><strong>Example 2:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> x = -123 | ||
| <strong>Output:</strong> -321 | ||
| </pre> | ||
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| <p><strong>Example 3:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> x = 120 | ||
| <strong>Output:</strong> 21 | ||
| </pre> | ||
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| <p> </p> | ||
| <p><strong>Constraints:</strong></p> | ||
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| <ul> | ||
| <li><code>-2<sup>31</sup> <= x <= 2<sup>31</sup> - 1</code></li> | ||
| </ul> |
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| # Question Description | ||
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| <p>Implement the <code>myAtoi(string s)</code> function, which converts a string to a 32-bit signed integer (similar to C/C++'s <code>atoi</code> function).</p> | ||
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| <p>The algorithm for <code>myAtoi(string s)</code> is as follows:</p> | ||
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| <ol> | ||
| <li>Read in and ignore any leading whitespace.</li> | ||
| <li>Check if the next character (if not already at the end of the string) is <code>'-'</code> or <code>'+'</code>. Read this character in if it is either. This determines if the final result is negative or positive respectively. Assume the result is positive if neither is present.</li> | ||
| <li>Read in next the characters until the next non-digit character or the end of the input is reached. The rest of the string is ignored.</li> | ||
| <li>Convert these digits into an integer (i.e. <code>"123" -> 123</code>, <code>"0032" -> 32</code>). If no digits were read, then the integer is <code>0</code>. Change the sign as necessary (from step 2).</li> | ||
| <li>If the integer is out of the 32-bit signed integer range <code>[-2<sup>31</sup>, 2<sup>31</sup> - 1]</code>, then clamp the integer so that it remains in the range. Specifically, integers less than <code>-2<sup>31</sup></code> should be clamped to <code>-2<sup>31</sup></code>, and integers greater than <code>2<sup>31</sup> - 1</code> should be clamped to <code>2<sup>31</sup> - 1</code>.</li> | ||
| <li>Return the integer as the final result.</li> | ||
| </ol> | ||
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| <p><strong>Note:</strong></p> | ||
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| <ul> | ||
| <li>Only the space character <code>' '</code> is considered a whitespace character.</li> | ||
| <li><strong>Do not ignore</strong> any characters other than the leading whitespace or the rest of the string after the digits.</li> | ||
| </ul> | ||
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| <p> </p> | ||
| <p><strong>Example 1:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = "42" | ||
| <strong>Output:</strong> 42 | ||
| <strong>Explanation:</strong> The underlined characters are what is read in, the caret is the current reader position. | ||
| Step 1: "42" (no characters read because there is no leading whitespace) | ||
| ^ | ||
| Step 2: "42" (no characters read because there is neither a '-' nor '+') | ||
| ^ | ||
| Step 3: "<u>42</u>" ("42" is read in) | ||
| ^ | ||
| The parsed integer is 42. | ||
| Since 42 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is 42. | ||
| </pre> | ||
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| <p><strong>Example 2:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = " -42" | ||
| <strong>Output:</strong> -42 | ||
| <strong>Explanation:</strong> | ||
| Step 1: "<u> </u>-42" (leading whitespace is read and ignored) | ||
| ^ | ||
| Step 2: " <u>-</u>42" ('-' is read, so the result should be negative) | ||
| ^ | ||
| Step 3: " -<u>42</u>" ("42" is read in) | ||
| ^ | ||
| The parsed integer is -42. | ||
| Since -42 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is -42. | ||
| </pre> | ||
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| <p><strong>Example 3:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> s = "4193 with words" | ||
| <strong>Output:</strong> 4193 | ||
| <strong>Explanation:</strong> | ||
| Step 1: "4193 with words" (no characters read because there is no leading whitespace) | ||
| ^ | ||
| Step 2: "4193 with words" (no characters read because there is neither a '-' nor '+') | ||
| ^ | ||
| Step 3: "<u>4193</u> with words" ("4193" is read in; reading stops because the next character is a non-digit) | ||
| ^ | ||
| The parsed integer is 4193. | ||
| Since 4193 is in the range [-2<sup>31</sup>, 2<sup>31</sup> - 1], the final result is 4193. | ||
| </pre> | ||
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| <p> </p> | ||
| <p><strong>Constraints:</strong></p> | ||
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| <ul> | ||
| <li><code>0 <= s.length <= 200</code></li> | ||
| <li><code>s</code> consists of English letters (lower-case and upper-case), digits (<code>0-9</code>), <code>' '</code>, <code>'+'</code>, <code>'-'</code>, and <code>'.'</code>.</li> | ||
| </ul> |
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| # Question Description | ||
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| <p>Given an integer <code>x</code>, return <code>true</code> if <code>x</code> is palindrome integer.</p> | ||
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| <p>An integer is a <strong>palindrome</strong> when it reads the same backward as forward.</p> | ||
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| <ul> | ||
| <li>For example, <code>121</code> is a palindrome while <code>123</code> is not.</li> | ||
| </ul> | ||
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| <p> </p> | ||
| <p><strong>Example 1:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> x = 121 | ||
| <strong>Output:</strong> true | ||
| <strong>Explanation:</strong> 121 reads as 121 from left to right and from right to left. | ||
| </pre> | ||
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| <p><strong>Example 2:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> x = -121 | ||
| <strong>Output:</strong> false | ||
| <strong>Explanation:</strong> From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome. | ||
| </pre> | ||
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| <p><strong>Example 3:</strong></p> | ||
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| <pre> | ||
| <strong>Input:</strong> x = 10 | ||
| <strong>Output:</strong> false | ||
| <strong>Explanation:</strong> Reads 01 from right to left. Therefore it is not a palindrome. | ||
| </pre> | ||
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| <p> </p> | ||
| <p><strong>Constraints:</strong></p> | ||
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| <ul> | ||
| <li><code>-2<sup>31</sup> <= x <= 2<sup>31</sup> - 1</code></li> | ||
| </ul> | ||
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| <p> </p> | ||
| <strong>Follow up:</strong> Could you solve it without converting the integer to a string? |
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