分类讨论。比较暴力``` class Solution { public: int minOperations(string s) { auto t = s; sort(t.begin(),t.end()); if(s == t) { return 0; } int n = s.size(); auto minv = t[0]; auto maxv = t[n - 1]; if(minv == s

贪心``` class Solution { public: long long maxAlternatingSum(vector<int>& nums) { sort(nums.begin(),nums.end(),[](const int& a, const int &b) -> bool { return abs(a) < abs(b); }); long long res = 0; int

看到括号依旧喜欢递归，依旧把自己递归晕掉写半天。``` class Solution { public: int scoreOfParentheses(string s) { int n = s.size(); int idx = 0; auto solve = [&](this auto&& solve) -> int { if(idx >= n) { return 0; } if(s[idx]

两趟``` class Solution { public: bool checkValidString(string s) { int buffer_count = 0,diff = 0; int n = s.size(); for(int i = 0; i < n; i++) { if(s[i] == '*') { buffer_count++; } else if(s[i] == '(')

数据量小，蛮力插 `()` 了，也不知道为什么能过（还是dfs方法思路更清晰。``` class Solution { public: vector<string> generateParenthesis(int n) { vector<unordered_set<string>> v(n + 1,unordered_set<string>()); v[1].insert("()"); for(i