添加 0005.最长回文子串.md C语言解法

problems/0005.最长回文子串.md

@@ -462,7 +462,56 @@ var longestPalindrome = function(s) {
 };
 ```
 
+## C
+动态规划:
+```c
+//初始化dp数组，全部初始为false
+bool **initDP(int strLen) {
+    bool **dp = (bool **)malloc(sizeof(bool *) * strLen);
+    int i, j;
+    for(i = 0; i < strLen; ++i) {
+        dp[i] = (bool *)malloc(sizeof(bool) * strLen);
+        for(j = 0; j < strLen; ++j)
+            dp[i][j] = false;
+    }
+    return dp;
+}
 
+char * longestPalindrome(char * s){
+    //求出字符串长度
+    int strLen = strlen(s);
+    //初始化dp数组，元素初始化为false
+    bool **dp = initDP(strLen);
+    int maxLength = 0, left = 0, right = 0;
+
+    //从下到上，从左到右遍历
+    int i, j;
+    for(i = strLen - 1; i >= 0; --i) {
+        for(j = i; j < strLen; ++j) {
+            //若当前i与j所指字符一样
+            if(s[i] == s[j]) {
+                //若i、j指向相邻字符或同一字符，则为回文字符串
+                if(j - i <= 1)
+                    dp[i][j] = true;
+                //若i+1与j-1所指字符串为回文字符串，则i、j所指字符串为回文字符串
+                else if(dp[i + 1][j - 1])
+                    dp[i][j] = true;
+            }
+            //若新的字符串的长度大于之前的最大长度，进行更新
+            if(dp[i][j] && j - i + 1 > maxLength) {
+                maxLength = j - i + 1;
+                left = i;
+                right = j;
+            }
+        }
+    }
+    //复制回文字符串，并返回
+    char *ret = (char*)malloc(sizeof(char) * (maxLength + 1));
+    memcpy(ret, s + left, maxLength);
+    ret[maxLength] = 0;
+    return ret;
+}
+```
 
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