add 5. Longest Palindromic Substring

https://leetcode.com/problems/longest-palindromic-substring

Author: sayeed205

Medium/5. Longest Palindromic Substring/5. Longest Palindromic Substring.java

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+class Solution {
+    public String longestPalindrome(String s) {
+        int len = s.length();
+        
+        if (len <= 1) {
+            return s;
+        }
+        
+        boolean[][] dp = new boolean[len][len];
+        int start = 0;
+        int maxLen = 1;
+        
+        // All substrings of length 1 are palindromes.
+        for (int i = 0; i < len; i++) {
+            dp[i][i] = true;
+        }
+        
+        // Check for palindromes of length 2.
+        for (int i = 0; i < len - 1; i++) {
+            if (s.charAt(i) == s.charAt(i + 1)) {
+                dp[i][i + 1] = true;
+                start = i;
+                maxLen = 2;
+            }
+        }
+        
+        // Check for palindromes of length greater than 2.
+        for (int k = 3; k <= len; k++) {
+            for (int i = 0; i <= len - k; i++) {
+                int j = i + k - 1;
+                
+                if (dp[i + 1][j - 1] && s.charAt(i) == s.charAt(j)) {
+                    dp[i][j] = true;
+                    
+                    if (k > maxLen) {
+                        start = i;
+                        maxLen = k;
+                    }
+                }
+            }
+        }
+        
+        return s.substring(start, start + maxLen);
+    }
+}

Medium/5. Longest Palindromic Substring/5. Longest Palindromic Substring.js

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+/**
+ * @param {string} s
+ * @return {string}
+ */
+var longestPalindrome = function (s) {
+    const len = s.length;
+
+    if (len <= 1) {
+        return s;
+    }
+
+    let start = 0;
+    let maxLen = 1;
+
+    const dp = new Array(len).fill(false).map(() => new Array(len).fill(false));
+
+    // All substrings of length 1 are palindromes.
+    for (let i = 0; i < len; i++) {
+        dp[i][i] = true;
+    }
+
+    // Check for palindromes of length 2.
+    for (let i = 0; i < len - 1; i++) {
+        if (s[i] === s[i + 1]) {
+            dp[i][i + 1] = true;
+            start = i;
+            maxLen = 2;
+        }
+    }
+
+    // Check for palindromes of length greater than 2.
+    for (let k = 3; k <= len; k++) {
+        for (let i = 0; i <= len - k; i++) {
+            const j = i + k - 1;
+
+            if (dp[i + 1][j - 1] && s[i] === s[j]) {
+                dp[i][j] = true;
+
+                if (k > maxLen) {
+                    start = i;
+                    maxLen = k;
+                }
+            }
+        }
+    }
+
+    return s.substring(start, start + maxLen);
+};

Medium/5. Longest Palindromic Substring/5. Longest Palindromic Substring.py

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+class Solution:
+    def longestPalindrome(self, s: str) -> str:
+        def expandAroundCenter(left, right):
+            while left >= 0 and right < len(s) and s[left] == s[right]:
+                left -= 1
+                right += 1
+            return s[left + 1 : right]
+
+        longest = ""
+
+        for i in range(len(s)):
+            # Odd length palindrome
+            palindrome1 = expandAroundCenter(i, i)
+            if len(palindrome1) > len(longest):
+                longest = palindrome1
+
+            # Even length palindrome
+            palindrome2 = expandAroundCenter(i, i + 1)
+            if len(palindrome2) > len(longest):
+                longest = palindrome2
+
+        return longest

Medium/5. Longest Palindromic Substring/5. Longest Palindromic Substring.rs

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+impl Solution {
+    pub fn longest_palindrome(s: String) -> String {
+        let chars: Vec<char> = s.chars().collect();
+        let len = chars.len();
+
+        if len <= 1 {
+            return s;
+        }
+
+        let mut dp = vec![vec![false; len]; len];
+        let mut start = 0;
+        let mut max_len = 1;
+
+        // All substrings of length 1 are palindromes.
+        for i in 0..len {
+            dp[i][i] = true;
+        }
+
+        // Check for palindromes of length 2.
+        for i in 0..len - 1 {
+            if chars[i] == chars[i + 1] {
+                dp[i][i + 1] = true;
+                start = i;
+                max_len = 2;
+            }
+        }
+
+        // Check for palindromes of length greater than 2.
+        for k in 3..=len {
+            for i in 0..(len - k + 1) {
+                let j = i + k - 1;
+
+                if dp[i + 1][j - 1] && chars[i] == chars[j] {
+                    dp[i][j] = true;
+
+                    if k > max_len {
+                        start = i;
+                        max_len = k;
+                    }
+                }
+            }
+        }
+
+        chars[start..start + max_len].iter().collect()
+    }
+}

Medium/5. Longest Palindromic Substring/5. Longest Palindromic Substring.ts

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+function longestPalindrome(s: string): string {
+    const len = s.length;
+
+    if (len <= 1) {
+        return s;
+    }
+
+    let start = 0;
+    let maxLen = 1;
+
+    const dp: boolean[][] = new Array(len)
+        .fill(0)
+        .map(() => new Array(len).fill(false));
+
+    // All substrings of length 1 are palindromes.
+    for (let i = 0; i < len; i++) {
+        dp[i][i] = true;
+    }
+
+    // Check for palindromes of length 2.
+    for (let i = 0; i < len - 1; i++) {
+        if (s[i] === s[i + 1]) {
+            dp[i][i + 1] = true;
+            start = i;
+            maxLen = 2;
+        }
+    }
+
+    // Check for palindromes of length greater than 2.
+    for (let k = 3; k <= len; k++) {
+        for (let i = 0; i <= len - k; i++) {
+            const j = i + k - 1;
+
+            if (dp[i + 1][j - 1] && s[i] === s[j]) {
+                dp[i][j] = true;
+
+                if (k > maxLen) {
+                    start = i;
+                    maxLen = k;
+                }
+            }
+        }
+    }
+
+    return s.substring(start, start + maxLen);
+}

Medium/5. Longest Palindromic Substring/README.md

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+## [5. Longest Palindromic Substring](https://leetcode.com/problems/longest-palindromic-substring)
+
+Given a string `s`, return _the longest
+palindromic substring in `s`_.
+
+#### Example 1:
+
+<pre>
+<strong>Input:</strong> s = "babad"
+<strong>Output:</strong> "bab"
+<strong>Explanation:</strong> "aba" is also a valid answer.
+</pre>
+
+#### Example 2:
+
+<pre>
+<strong>Input:</strong> s = "cbbd"
+<strong>Output:</strong> "bb"
+</pre>
+
+#### Constraints:
+
+-   `1 <= s.length <= 1000`
+-   `s` consist of only digits and English letters.