Add Longest Palindromic Substring in C (#4353)

Author: 2Clutch

archive/c/c/longest-palindromic-substring.c

@@ -0,0 +1,61 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdbool.h>
+
+#define MAX_LENGTH 1000
+
+int expandAroundCenter(const char* s, int left, int right) {
+    while (left >= 0 && right < strlen(s) && s[left] == s[right]) {
+        left--;
+        right++;
+    }
+    return right - left - 1;
+}
+
+bool longestPalindromicSubstring(const char* s, char* result) {
+    if (s == NULL || strlen(s) == 0) {
+        strcpy(result, "");
+        return false;
+    }
+
+    int start = 0, maxLength = 0;
+    int len = strlen(s);
+
+    for (int i = 0; i < len; i++) {
+        int len1 = expandAroundCenter(s, i, i);
+        int len2 = expandAroundCenter(s, i, i + 1);
+        int len = (len1 > len2) ? len1 : len2;
+
+        if (len > maxLength) {
+            start = i - (len - 1) / 2;
+            maxLength = len;
+        }
+    }
+
+    if (maxLength > 1) {
+        strncpy(result, s + start, maxLength);
+        result[maxLength] = '\0';
+        return true;
+    }
+
+    strcpy(result, "");
+    return false;
+}
+
+int main(int argc, char* argv[]) {
+    if (argc != 2) {
+        printf("Usage: please provide a string that contains at least one palindrome\n");
+        return 1;
+    }
+
+    const char* input = argv[1];
+    char result[MAX_LENGTH];
+
+    if (longestPalindromicSubstring(input, result) && strlen(result) > 0) {
+        printf("%s\n", result);
+    } else {
+        printf("Usage: please provide a string that contains at least one palindrome\n");
+    }
+
+    return 0;
+}