leetcode题目例题解析(五)
Generate Parentheses
题目描述:
Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses. For example, given n = 3, a solution set is:
[
“((()))”,
“(()())”,
“(())()”,
“()(())”,
“()()()”
]
题意解析:
这道题并不复杂,只要通过排列组合的形式,括号匹配,保证每一个右括号都有一个相应的左括号
解题思路:
通过递归,每一层添加一个左括号或者右括号,并判断是否可以添加,最后的判断条件是左括号和右括号的数量都为n
代码:
class Solution {
public:
/*这里now是当前完成的字符串,每层都传到下层的都一样,所以不用引用传递*/
void find(vector<string>& ans, int a, int b, int n, string now) {
if (a < n && b < n) {
now = now + '(';
string temp = now;
find(ans, a + 1, b, n, now); //连续添加左括号
for (int j = b + 1; j <= a + 1; j++) {
temp = temp + ')';
find(ans, a + 1, j, n, temp);
}
} else if (a == n&&b == n) {
ans.push_back(now);
}
}
vector<string> generateParenthesis(int n) {
vector<string> ans;
string now = "";
find(ans, 0, 0, n, now);
return ans;
}
};
原题目链接:
https://leetcode.com/problems/generate-parentheses/description/