16ms simple and neat c++ solution only using a vector. Detailed explanation

  • 29
    1. Initialize a vector called remaining, which contains the needed
      matching numbers of each character in s.
    2. If there are still
      characters needed to be contained (increment i in this case),
      decrease the matching number of that character and check if it is
      still non-negative. If it is, then it is the character in t, so
      decrease the total required number required.
    3. If there is no more
      characters required (increment start in this case), record min
      and left if a smaller length is found. Recover the number of this
      character in the remaining and if it is a character in t
      increase required.

    class Solution {
        string minWindow(string s, string t) {
            if (s.size() == 0 || t.size() == 0) return "";
            vector<int> remaining(128, 0);
            int required = t.size();
            for (int i = 0; i < required; i++) remaining[t[i]]++;
            // left is the start index of the min-length substring ever found
            int min = INT_MAX, start = 0, left = 0, i = 0;
            while(i <= s.size() && start < s.size()) {
                if(required) {
                    if (i == s.size()) break;
                    if (remaining[s[i]] >= 0) required--;
                } else {
                    if (i - start < min) {
                        min = i -start;
                        left = start;
                    if (remaining[s[start]] > 0) required++;
            return min == INT_MAX? "" : s.substr(left, min);

  • 0


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