一、题目内容

二、题解

解法1：

思路

全排列问题

代码

public class Solution {
    private ArrayList<String> ans = new ArrayList<String>();
    char[] c;
    public ArrayList<String> Permutation(String str) {
        c = str.toCharArray();
        recur(0);
        return ans;
    }
    /*
    a,b,c
    x=0       x=0
    i=x=0 ==> i=1
    */
    private void recur(int x){
        if(x == c.length -1 ){
            ans.add(String.valueOf(c));
            return;
        }
        HashSet<Character> set = new HashSet<>();
        for(int i = x;i<c.length;i++){
            if(set.contains(c[i])){
                //局域剪枝
                continue;
            }
            set.add(c[i]);
            swap(i,x);
            recur(x+1);
            swap(i,x);
        }
    }
    private void swap(int indexA,int indexB){
        char temp = c[indexA];
        c[indexA] = c[indexB];
        c[indexB] = temp;
    }
}