leetcode problem notes 76 minimum coverage substring

You are given a string  s , a string  t . Returns  the smallest substring s covering  t all characters in . Returns an empty string if  no  substring  s covering all characters exists in   .t""

Notice:

• For  t repeated characters, the number of characters in the substring we are looking for must be no less than the  t number of characters in the substring.
• If  s such a substring exists in , we guarantee that it is the only answer.

Idea 1: Sliding window

char * minWindow(char * s, char * t){
    int hash[58] = {0};
    int lenS = strlen(s);
    int lenT = strlen(t);
    int min = 0, max = INT_MAX; 
    for (int i = 0; i < lenT; ++i) hash[t[i] - 'A']++;
    for (int j = 0, i = 0; j < lenS; ++j) {
        if (hash[s[j] - 'A'] > 0) lenT--;
        hash[s[j] - 'A']--;
        while (lenT == 0) { 
             if (j - i + 1 < max - min + 1) {
                 max = j;
                 min = i;
             }
             if (++hash[s[i] - 'A'] > 0) lenT++;
             i++;
        }
    }
    if (max == INT_MAX) return "";
    char* res = malloc(sizeof(char) * (max - min + 2));
    int i = 0;
    while (min <= max) res[i++] = s[min++];
    res[i] = '\0';
    return res;
}

Time complexity O(n^2), space complexity O(n)

analyze:

First establish a hash table, store the number of each English letter in the hash table, subtract one from the corresponding position of the hash table according to the character of s[i], and constantly judge whether it is the smallest substring, and finally output the substring covering t

Summarize:

This question examines the application of sliding windows, and it can be solved by clearly writing the judgment of whether it is the smallest substring