LeetCode - Find All Anagrams in a String

Posted 2021-01-10 IncredibleThings

Given a string s and a non-empty string p, find all the start indices of p‘s anagrams in s.

Strings consists of lowercase English letters only and the length of both strings s and p will not be larger than 20,100.

The order of output does not matter.

Example 1:

Input:
s: "cbaebabacd" p: "abc"

Output:
[0, 6]

Explanation:
The substring with start index = 0 is "cba", which is an anagram of "abc".
The substring with start index = 6 is "bac", which is an anagram of "abc".
Example 2:

Input:
s: "abab" p: "ab"

Output:
[0, 1, 2]

Explanation:
The substring with start index = 0 is "ab", which is an anagram of "ab".
The substring with start index = 1 is "ba", which is an anagram of "ab".
The substring with start index = 2 is "ab", which is an anagram of "ab".

这道题先想到了用hash存一下p出现的字符和个数，然后遍历s来做。但超时了：

class Solution {
    public List<Integer> findAnagrams(String s, String p) {
        List<Integer> resList = new ArrayList<>();
        if(s == null || p == null){
            return resList;
        }
        Map<Character, Integer> map =new HashMap<>();
        for(char c : p.toCharArray()){
            map.put(c, map.getOrDefault(c,0)+1);
        }
        for(int i = 0; i <= s.length()-p.length(); i++){
            Map<Character, Integer> temp =new HashMap<>(map);
            for(int j = i; j < i + p.length(); j++){
                char c = s.charAt(j);
                if(temp.containsKey(c)){
                    int v = temp.get(c) - 1;
                    if(v < 0){
                        break;
                    }
                    temp.put(c,v);
                }
                else{break;}
            }
            boolean match = true;
            for(char c : temp.keySet()){
                if(temp.get(c) != 0){
                    match = false;
                    break;
                }
            }
            if(match){
                resList.add(i);
            }
        }
        return resList;
        
    }
}