又到了面试季，最近问了一个问题，好像不太好答，于是自己试试

leetcode 567 https://leetcode.com/problems/…

package test20190925.test20190925;

import java.util.Arrays;

public class SubStringCheck {

    public static String sortStringChar(String s) {
        char[] chars = s.toCharArray();
        Arrays.sort(chars);
        return new String(chars);
    }
    
    public static boolean checkContains(String s1, String s2) {
        String s1Sorted = sortStringChar(s1);
        //System.out.println(s1Sorted);
        int s1Length = s1Sorted.length();
        int s2Length = s2.length();
        for (int i = 0; i <= s2Length - s1Length; i++) {
            String s2Capture = s2.substring(i, i + s1Length);
            //System.out.println(s2Capture);
            String s2CaptureSorted = sortStringChar(s2Capture);
            if (s1Sorted.equals(s2CaptureSorted)) {
                return true;
            }
        }
        return false;
    }
    
    public static void main(String[] args) {
        System.out.println(checkContains("abc", "eidboaoo"));
    }

}

2021-9-30 又搞了一个 c++ 的，这个快很多，内存也小

class Solution {
public:
    bool checkInclusion(string s1, string s2) {        
        vector<int> s1count(26), s2count(26);
        for (size_t i = 0; i < s1.length() && i < s2.length(); i++) {
            s1count[s1.at(i) - 'a']++;
            s2count[s2.at(i) - 'a']++;
        }
        for (size_t i = s1.length() - 1; i < s2.length(); i++) {
            if (s1count == s2count) {
                return true;
            }
            if (i + 1 < s2.length()) {
                s2count[s2.at(i - s1.length() + 1) - 'a']--;
                s2count[s2.at(i + 1) - 'a']++;
            }
        }
        return false;
    }
    
};

2024-1-18 补充了一个 Java 版本的数组实现

package com.test20231227;

import java.util.Arrays;
import java.util.Date;

public class SubStringCheck {
    public static boolean checkInclusion(String s1, String s2) {
        int[] s1count = new int[26];
        int[] s2count = new int[26];
        final int ascii_char_a = (int)'a';
        for (int i = 0; i < s1.length() && i < s2.length(); i++) {
            s1count[(int)s1.charAt(i) - ascii_char_a]++;
            s2count[(int)s2.charAt(i) - ascii_char_a]++;
        }
        for (int i = s1.length() - 1; i < s2.length(); i++) {
            if (Arrays.equals(s1count, s2count)) {
                return true;
            }
            if (i + 1 < s2.length()) {
                s2count[(int)s2.charAt(i - s1.length() + 1) - ascii_char_a]--;
                s2count[(int)s2.charAt(i + 1) - ascii_char_a]++;
            }
        }
        return false;
    }
    
    public static void main(String[] args) {
        System.out.println(checkInclusion("abcd", "eidcboaoo"));
    }
}