[Wonjuny0804] WEEK 03 solutions

combination-sum/Wonjuny0804.ts

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+function combinationSum(candidates: number[], target: number): number[][] {
+  const result: number[][] = [];
+
+  const dfs = (start: number, target: number, path: number[]) => {
+      if (target === 0) {
+          result.push([...path]);
+          return;
+      }
+
+      for (let i = start; i < candidates.length; i++) {
+          if (candidates[i] > target) continue;
+
+          path.push(candidates[i]);
+          dfs(i, target - candidates[i], path);
+          path.pop();
+      }
+  }
+
+  candidates.sort((a, b) => a - b);
+  dfs(0, target, []);
+  return result;
+};

decode-ways/Wonjuny0804.ts

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+function numDecodings(s: string): number {
+  const memo: Record<number, number> = {};
+
+  const dfs = (index: number): number => {
+      if (index === s.length) return 1;
+      if (s[index] === '0') return 0;
+
+      if (memo[index] !== undefined) return memo[index];
+
+      let res = dfs(index + 1);
+
+      if (index + 1 < s.length && Number(s.slice(index, index + 2)) <= 26) {
+          res += dfs(index + 2);
+      }
+
+      memo[index] = res;
+      return res;
+  }
+
+  return dfs(0);
+}

maximum-subarray/Wonjuny0804.ts

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+function maxSubArray(nums: number[]): number {
+  const n = nums.length;
+  const dp = new Array(n).fill(0);
+  dp[0] = nums[0];
+  let result = dp[0];
+
+  for (let i = 1; i < n; i++) {
+      dp[i] = Math.max(nums[i], dp[i - 1] + nums[i]);
+      result = Math.max(result, dp[i]);
+  }
+
+  return result;
+}

number-of-1-bits/Wonjuny0804.ts

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+function hammingWeight(n: number): number {
+  return n
+    .toString(2)
+    .split("")
+    .reduce((acc, i) => acc + +i, 0);
+}

two-sum/Wonjuny0804.ts

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+/*
+
+    Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
+    You may assume that each input would have exactly one solution, and you may not use the same element twice.
+    You can return the answer in any order.
+
+    Example 1:
+
+    Input: nums = [2,7,11,15], target = 9
+    Output: [0,1]
+    Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].
+
+    Example 2:
+
+    Input: nums = [3,2,4], target = 6
+    Output: [1,2]
+
+    Example 3:
+
+    Input: nums = [3,3], target = 6
+    Output: [0,1]
+
+*/
+
+function twoSum(nums: number[], target: number): number[] {
+  const map = new Map();
+
+  for (let i = 0; i < nums.length; i++) {
+    const diff = target - nums[i];
+    if (map.has(nums[i])) return [map.get(nums[i]), i];
+    else map.set(diff, i);
+  }
+
+  return [];
+}

valid-palindrome/Wonjuny0804.ts

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+function isPalindrome(s: string): boolean {
+  const lowered = s.toLowerCase();
+  const removed = lowered.replaceAll(
+    /[!|\s|.\\|\|()@#$%^&*_\-+,:'"\[\]{}\?;`]/g,
+    ""
+  );
+
+  for (let i = 0; i < removed.length; i++) {
+    if (removed[i] !== removed[removed.length - i - 1]) return false;
+  }
+  return true;
+}