【Leetcode打卡】递归回溯

784. 字母大小写全排列

class Solution {
public:int find(string s,int pos){int i=pos;while(i<s.size()){if(isalpha(s[i])){return i;}++i;}return -1;}void turn(string& s,int pos){if(islower(s[pos])){s[pos]=toupper(s[pos]);}else{s[pos]=tolower(s[pos]);}}vector<string> save;void dfs(string s,int pos){pos=find(s,pos);if(pos==-1){save.push_back(s);return;}//说明有字母       turn(s,pos); dfs(s,pos+1);turn(s,pos);dfs(s,pos+1);}vector<string> letterCasePermutation(string s) {dfs(s,0);return save;}
};

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LCR 081. 组合总和

class Solution {
public:vector<vector<int> > save;int sum=0;vector<int> path;void dfs(vector<int>& v,int target,int pos){if(sum==target){save.push_back(path);return;}if(sum>target){return;}for(int i=pos;i<v.size();++i){sum+=v[i];path.push_back(v[i]);dfs(v,target,i);path.pop_back();sum-=v[i];}}vector<vector<int>> combinationSum(vector<int>& candidates, int target) {sort(candidates.begin(),candidates.end());dfs(candidates,target,0);return save;}
};