Minimum Window Substring
Desicription
Given a string S and a string T, find the minimum window in S which will contain all the characters in T in complexity O(n).
For example,
S = "ADOBECODEBANC"
T = "ABC"
Minimum window is "BANC"
.
Note:
If there is no such window in S that covers all characters in T, return the empty string ""
.
If there are multiple such windows, you are guaranteed that there will always be only one unique minimum window in S.
Solution
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 class Solution { public: string minWindow(string s, string t) { if(s.empty()  t.empty()) return ""; int cnt = t.size(); vector<int> require(128, 0); vector<bool> book(128, 0); for(int i = 0; t[i]; ++i) require[t[i]]++, book[t[i]] = 1; int left = 0; int right = 1; int min_len = INT_MAX; int min_index = 0; while(left < s.size() && right < (int)s.size()){ if(cnt){ require[s[++right]]; if(book[s[right]] && require[s[right]] >= 0) cnt; } else{ if(min_len > right  left + 1) min_len = right  left + 1, min_index = left; require[s[left]]++; if(book[s[left]] && require[s[left]] > 0) cnt++; left++; } } if(min_len == INT_MAX) return ""; return s.substr(min_index, min_len); } };
