输入一个字符串,打印出该字符串中字符的所有排列。
你可以以任意顺序返回这个字符串数组,但里面不能有重复元素。
典型的全排列问题,根据字符串排列的特点,考虑深度优先搜索所有排列方案。即通过字符交换,先固定第 1 位字符( n 种情况)、再固定第 2 位字符( n−1 种情况)、... 、最后固定第 n 位字符( 1 种情况)。 力扣
当字符串存在重复字符时,排列方案中也存在重复的排列方案。为排除重复方案,需在固定某位字符时,保证 “每种字符只在此位固定一次” ,即遇到重复字符时不交换,直接跳过。从 DFS 角度看,此操作称为 “剪枝” 。
import java.util.Scanner;
import java.util.*;
import java.util.stream.Collectors;
import java.math.BigInteger;
import java.util.stream.Stream;
class Main {
public static List<String> res = new LinkedList<>();
public static char[] c;
public static void main(String[] args) {
// 处理输入
Scanner in = new Scanner(System.in);
String input_str = in.nextLine();
System.out.println(Arrays.toString(permutation(input_str)));
}
public static String[] permutation(String s) {
c = s.toCharArray();
dfs(0);
return res.toArray(new String[res.size()]);
}
public static void dfs(int x) {
if(x == c.length - 1) {
res.add(String.valueOf(c)); // 添加排列方案
return;
}
HashSet<Character> set = new HashSet<>();
for(int i = x; i < c.length; i++) {
if(set.contains(c[i])) continue; // 重复,因此剪枝
set.add(c[i]);
swap(i, x); // 交换,将 c[i] 固定在第 x 位
dfs(x + 1); // 开启固定第 x + 1 位字符
swap(i, x); // 恢复交换
}
}
public static void swap(int a, int b) {
char tmp = c[a];
c[a] = c[b];
c[b] = tmp;
}
}
华为OD 2023/2022 最新机试题及讲解,100%通过率。
Java: https://renjie.blog.csdn.net/article/details/127947829
Python: https://renjie.blog.csdn.net/article/details/127946125
C++: https://renjie.blog.csdn.net/article/details/126965954
Js: https://renjie.blog.csdn.net/article/details/128974467
C: https://renjie.blog.csdn.net/article/details/129190260
华为OD 2023/2022 最新机试题及讲解,100%通过率。
Java: https://renjie.blog.csdn.net/article/details/127947829
Python: https://renjie.blog.csdn.net/article/details/127946125
C++: https://renjie.blog.csdn.net/article/details/126965954
Js: https://renjie.blog.csdn.net/article/details/128974467
C: https://renjie.blog.csdn.net/article/details/129190260
华为OD 2023/2022 最新机试题及讲解,100%通过率。
Java: https://renjie.blog.csdn.net/article/details/127947829
Python: https://renjie.blog.csdn.net/article/details/127946125
C++: https://renjie.blog.csdn.net/article/details/126965954
Js: https://renjie.blog.csdn.net/article/details/128974467