feat: add Longest Valid Parentheses LeetCode problem (#1166)

Co-authored-by: David Leal <halfpacho@gmail.com>

leetcode/DIRECTORY.md

@@ -24,6 +24,7 @@
 | 27   | [Remove Element](https://leetcode.com/problems/remove-element/)                                                                 | [C](./src/27.c)   | Easy       |
 | 28   | [Implement strStr()](https://leetcode.com/problems/implement-strstr/)                                                           | [C](./src/28.c)   | Easy       |
 | 29   | [Divide Two Integers](https://leetcode.com/problems/divide-two-integers/)                                                       | [C](./src/29.c)   | Medium     |
+| 32   | [Longest Valid Parentheses](https://leetcode.com/problems/longest-valid-parentheses/)                                           | [C](./src/32.c)   | Hard       |
 | 35   | [Search Insert Position](https://leetcode.com/problems/search-insert-position/)                                                 | [C](./src/35.c)   | Easy       |
 | 38   | [Count and Say](https://leetcode.com/problems/count-and-say/)                                                                   | [C](./src/38.c)   | Easy       |
 | 42   | [Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/)                                                       | [C](./src/42.c)   | Hard       |

leetcode/src/32.c

@@ -0,0 +1,60 @@
+#define max(x,y)(((x)>(y))?(x):(y))
+
+const int notCalculated = -2;
+const int notValid = -1;
+
+int getEndValidIndexFromDp(int* dp, char* s, int index, int lenS){
+    if (index >= lenS){
+        return notValid;
+    }
+
+    if (dp[index] == notCalculated){
+        dp[index] = getEndValidIndex(dp, s, index, lenS);
+    }
+
+    return dp[index];
+}
+
+int getEndValidIndex(int* dp, char* s, int index, int lenS){
+    if (s[index] == '('){
+        if (index + 1 >= lenS){
+            return notValid;
+        }
+
+        if (s[index + 1] == ')'){
+            return max(index + 1, getEndValidIndexFromDp(dp, s, index + 2, lenS));
+        }
+        
+        int nextEndValidIndex = getEndValidIndexFromDp(dp, s, index + 1, lenS);
+        if (nextEndValidIndex == notValid || nextEndValidIndex + 1 >= lenS || s[nextEndValidIndex + 1] != ')') {
+            return notValid;
+        }
+        
+        return max(nextEndValidIndex + 1, getEndValidIndexFromDp(dp, s, nextEndValidIndex + 2, lenS));
+    }
+    
+    return notValid;
+}
+
+// Dynamic Programming. UP -> down approach.
+// Runtime: O(n)
+// Space: O(n)
+int longestValidParentheses(char * s){
+    int lenS = strlen(s);
+    if (lenS == 0){
+        return 0;
+    }
+
+    int* dp = malloc(lenS * sizeof(int));
+    for(int i = 0; i < lenS; i++){
+        dp[i] = notCalculated;
+    }
+
+    int result = 0;
+    for(int i = 0; i < lenS; i++){
+        result = max(result, getEndValidIndexFromDp(dp, s, i, lenS) - i + 1);
+    }
+    
+    free(dp);
+    return result;
+}