题解 | 字符串的排列

class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param str string字符串 
     * @return string字符串vector
     */
    vector<string> ans;
    string path;
    vector<bool> st;

    vector<string> Permutation(string str) {
        if (str.empty()) return {};
        sort(str.begin(), str.end());
        path.resize(str.size());
        st = vector<bool> (str.size());
        dfs(str, 0);
        return ans;
    }

    void dfs(string &str, int u) {
        if (u == str.size()) ans.push_back(path);
        for (int i = 0; i < str.size(); i++) {
            if (!st[i]) {
                if (i && str[i - 1] == str[i] && st[i - 1]) continue;
                path[u] = str[i];
                st[i] = true;
                dfs(str, u + 1);
                st[i] = false;
            }
        }
    }
};