1239_maxLength.txt

class Solution {
    int res = 0;
    int visited[26] = {0};
    string str;

public:
    int maxLength(vector<string>& arr) {
        dfs(arr,0);
        return res;
    }
    void dfs(vector<string>& arr, int start){
        for(int i = start;i<arr.size();i++){
            int temp[26] = {0};
            int flag = 1;
            for(int j = 0;j<arr[i].size();j++){
                //该字符串自己出现重复字符或者跟str存在相同字符则不可备选
                if(visited[arr[i][j]-'a'] || temp[arr[i][j]-'a']){
                    flag = 0;
                    break;
                }
                temp[arr[i][j]-'a'] = 1;
            }

            if(flag){
                str += arr[i];
                for(int j = 0;j<arr[i].size();j++)
                    visited[arr[i][j]-'a'] = 1;
                dfs(arr,i+1);
                //回溯恢复状态
                for(int j = 0;j<arr[i].size();j++){
                    visited[arr[i][j]-'a'] = 0;
                    str.pop_back();
                }   
            }
        }
        int len = str.size();
        res = max(len,res);
        return;
    }
};