[Oracle] LeetCode 76 Minimum Window Substring 双指针

Given two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring, return the empty string "".

The testcases will be generated such that the answer is unique.

A substring is a contiguous sequence of characters within the string.

Solution

我们首先用 \(map\) 来记录 \(t\) 中字符出现的次数。然后用左右指针分别移动

点击查看代码

class Solution {
private:
    string ans="";
    unordered_map<char,int> mp;
    int min_len=INT_MAX;
    int st_ans=0;
public:
    string minWindow(string s, string t) {
        int m = s.size(), n = t.size();
        if(m<n)return ans;
        int l=0,h=0;
        int cnt=0;
        for(auto ele:t)mp[ele]++;
        for(h=0;h<m;h++){
            if(mp[s[h]]>0)cnt++;//means that this letter is in t
            mp[s[h]]--;
            if(cnt==n){
                while(l<h && mp[s[l]]<0){mp[s[l]]++;l++;}
                if(min_len>h-l+1){
                    min_len = h-l+1;st_ans=l;
                }
                mp[s[l]]++;l++;
                cnt--;
            }
        }
        return min_len==INT_MAX?"":s.substr(st_ans,min_len);
    }
};