LongestpalindromicSubstring in Java and python

Leetcode-Medium/5-LongestPalindromicSubstring/solutionInJava.java

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+class Solution {
+    public String longestPalindrome(String s) {
+        char[] sChars = s.toCharArray();
+
+        int m = s.length();
+
+        // * dp[i][len + 1] means substring starting from i with length of len;
+        boolean[][] dp = new boolean[m][2];
+        int currCol = 0;
+
+        int maxLen = 0;
+        int ans = 0; // record start index of s
+
+        for (int len = 0; len < m; len++) {
+            for (int start = 0; start + len < m; start++) {
+                int end = start + len;
+                if (len == 0) {
+                    dp[start][currCol] = true;
+                } else if (len == 1) {
+                    dp[start][currCol] = (sChars[start] == sChars[end]);
+                } else {
+                    dp[start][currCol] = (sChars[start] == sChars[end] && dp[start + 1][currCol]);
+                }
+
+                if (dp[start][currCol] && len + 1 > maxLen) {
+                    ans = start;
+                    maxLen = len + 1;
+                }
+            }
+
+            currCol = 1 - currCol;
+        }
+
+        return maxLen == 0 ? "" : s.substring(ans, ans + maxLen);
+    }
+}

Leetcode-Medium/5-LongestPalindromicSubstring/solutioninpython.py

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+class Solution:
+    def longestPalindrome(self, s: str) -> str:
+
+        n = len(s)
+        # Form a bottom-up dp 2d array
+        # dp[i][j] will be 'true' if the string from index i to j is a palindrome. 
+        dp = [[False] * n  for _ in range(n)]
+
+        ans = ''
+        # every string with one character is a palindrome
+        for i in range(n):
+            dp[i][i] = True
+            ans = s[i]
+
+        maxLen = 1
+        for start in range(n-1, -1, -1):
+            for end in range(start+1, n):             
+				# palindrome condition
+                if s[start] == s[end]:
+                    # if it's a two char. string or if the remaining string is a palindrome too
+                    if end - start == 1 or dp[start+1][end-1]:
+                        dp[start][end] = True
+                        if maxLen < end - start + 1:
+                            maxLen = end - start + 1
+                            ans = s[start: end+ 1]
+
+        return ans

Leetcode-Medium/946-validate-stack-sequences/solution.java

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+public boolean validateStackSequences(int[] pushed, int[] popped) {
+    Stack<Integer> stack = new Stack<>();
+    int i = 0;
+    for (int x : pushed) {
+        stack.push(x);
+        while (!stack.empty() && stack.peek() == popped[i]) {
+            stack.pop();
+            i++;
+        }
+    }
+    return stack.empty();
+}