Update Solution.c

Author: yanglbme

solution/0000-0099/0005.Longest Palindromic Substring/Solution.c

@@ -1,45 +1,31 @@
-
-
 char* longestPalindrome(char* s) {
     int n = strlen(s);
-    if (n == 0) {
-        char* result = malloc(1);
-        result[0] = '\0';
-        return result;
-    }
-
-    bool dp[n][n];
-    memset(dp, 0, sizeof(dp));
-
-    int start = 0, max_len = 1;
-
-    for (int i = 0; i < n; i++) {
-        dp[i][i] = true;
-    }
-
-    for (int i = 0; i < n - 1; i++) {
-        if (s[i] == s[i + 1]) {
-            dp[i][i + 1] = true;
-            start = i;
-            max_len = 2;
+    bool** f = (bool**) malloc(n * sizeof(bool*));
+    for (int i = 0; i < n; ++i) {
+        f[i] = (bool*) malloc(n * sizeof(bool));
+        for (int j = 0; j < n; ++j) {
+            f[i][j] = true;
         }
     }
-
-    // Check for lengths > 2
-    for (int len = 3; len <= n; len++) {
-        for (int i = 0; i < n - len + 1; i++) {
-            int j = i + len - 1;
-            if (s[i] == s[j] && dp[i + 1][j - 1]) {
-                dp[i][j] = true;
-                if (len > max_len) {
-                    start = i;
-                    max_len = len;
+    int k = 0, mx = 1;
+    for (int i = n - 2; ~i; --i) {
+        for (int j = i + 1; j < n; ++j) {
+            f[i][j] = false;
+            if (s[i] == s[j]) {
+                f[i][j] = f[i + 1][j - 1];
+                if (f[i][j] && mx < j - i + 1) {
+                    mx = j - i + 1;
+                    k = i;
                 }
             }
         }
     }
-    char* result = malloc(max_len + 1);
-    strncpy(result, s + start, max_len);
-    result[max_len] = '\0';
-    return result;
+    char* res = (char*) malloc((mx + 1) * sizeof(char));
+    strncpy(res, s + k, mx);
+    res[mx] = '\0';
+    for (int i = 0; i < n; ++i) {
+        free(f[i]);
+    }
+    free(f);
+    return res;
 }