题目：

题解：

// 回溯法求解
#define MAX_SIZE 1430  // 卡特兰数: 1, 1, 2, 5, 14, 42, 132, 429, 1430
void generate(int left, int right, int n, char *str, int index, char **result, int *returnSize) {if (index == 2 * n) { // 当前长度已达2nresult[(*returnSize)] =  (char*)calloc((2 * n + 1), sizeof(char));strcpy(result[(*returnSize)++], str);return;}// 如果左括号数量不大于 n，可以放一个左括号if (left < n) {str[index] = '(';generate(left + 1, right, n, str, index + 1, result, returnSize);}// 如果右括号数量小于左括号的数量，可以放一个右括号if (right < left) {str[index] = ')';generate(left, right + 1, n, str, index + 1, result, returnSize);}
}
/*** Note: The returned array must be malloced, assume caller calls free().*/
char** generateParenthesis(int n, int *returnSize) {char *str = (char*)calloc((2 * n + 1), sizeof(char));char **result = (char **)malloc(sizeof(char *) * MAX_SIZE);*returnSize = 0;generate(0, 0, n, str, 0, result, returnSize);return result;
}