76. Minimum Window Substring

public class Solution {
    public string MinWindow(string s, string t) {
        if (s.Length == 0 || t.Length == 0) {
            return "";
        }
        Dictionary<char, int> dictT = new Dictionary<char, int>();
        for (int i = 0; i < t.Length; i++) {
            if (dictT.ContainsKey(t[i])) {
                dictT[t[i]]++;
            } else {
                dictT[t[i]] = 1;
            }
        }
        int required = dictT.Count;
        int l = 0, r = 0;
        int formed = 0;
        Dictionary<char, int> windowCounts = new Dictionary<char, int>();
        int[] ans = { -1, 0, 0 };
        while (r < s.Length) {
            char c = s[r];
            if (windowCounts.ContainsKey(c)) {
                windowCounts[c]++;
            } else {
                windowCounts[c] = 1;
            }
            if (dictT.ContainsKey(c) && windowCounts[c] == dictT[c]) {
                formed++;
            }
            while (l <= r && formed == required) {
                c = s[l];
                if (ans[0] == -1 || r - l + 1 < ans[0]) {
                    ans[0] = r - l + 1;
                    ans[1] = l;
                    ans[2] = r;
                }
                windowCounts[c]--;
                if (dictT.ContainsKey(c) && windowCounts[c] < dictT[c]) {
                    formed--;
                }
                l++;
            }
            r++;
        }
        return ans[0] == -1 ? "" : s.Substring(ans[1], ans[2] - ans[1] + 1);
    }
}

#include <bits/stdc++.h>
using namespace std;

// Auto-generated C++ draft from the C# solution. Review containers, LINQ and helper types before submit.
class Solution {
public:
    public string MinWindow(string s, string t) {
        if (s.size() == 0 || t.size() == 0) {
            return "";
        }
        unordered_map<char, int> dictT = new unordered_map<char, int>();
        for (int i = 0; i < t.size(); i++) {
            if (dictT.count(t[i])) {
                dictT[t[i]]++;
            } else {
                dictT[t[i]] = 1;
            }
        }
        int required = dictT.size();
        int l = 0, r = 0;
        int formed = 0;
        unordered_map<char, int> windowCounts = new unordered_map<char, int>();
        vector<int>& ans = { -1, 0, 0 };
        while (r < s.size()) {
            char c = s[r];
            if (windowCounts.count(c)) {
                windowCounts[c]++;
            } else {
                windowCounts[c] = 1;
            }
            if (dictT.count(c) && windowCounts[c] == dictT[c]) {
                formed++;
            }
            while (l <= r && formed == required) {
                c = s[l];
                if (ans[0] == -1 || r - l + 1 < ans[0]) {
                    ans[0] = r - l + 1;
                    ans[1] = l;
                    ans[2] = r;
                }
                windowCounts[c]--;
                if (dictT.count(c) && windowCounts[c] < dictT[c]) {
                    formed--;
                }
                l++;
            }
            r++;
        }
        return ans[0] == -1 ? "" : s.Substring(ans[1], ans[2] - ans[1] + 1);
    }
}

class Solution {
    public String minWindow(String s, String t) {
        if (s.length() == 0 || t.length() == 0) {
            return "";
        }

        Map<Character, Integer> dictT = new HashMap<Character, Integer>();
        for (int i = 0; i < t.length(); i++) {
            int count = dictT.getOrDefault(t.charAt(i), 0);
            dictT.put(t.charAt(i), count + 1);
        }

        int required = dictT.size();
        int l = 0, r = 0;
        int formed = 0;
        Map<Character, Integer> windowCounts = new HashMap<Character, Integer>();
        int[] ans = { -1, 0, 0 };

        while (r < s.length()) {
            char c = s.charAt(r);
            int count = windowCounts.getOrDefault(c, 0);
            windowCounts.put(c, count + 1);

            if (dictT.containsKey(c) && windowCounts.get(c).intValue() == dictT.get(c).intValue()) {
                formed++;
            }

            while (l <= r && formed == required) {
                c = s.charAt(l);
                if (ans[0] == -1 || r - l + 1 < ans[0]) {
                    ans[0] = r - l + 1;
                    ans[1] = l;
                    ans[2] = r;
                }

                windowCounts.put(c, windowCounts.get(c) - 1);
                if (dictT.containsKey(c) && windowCounts.get(c).intValue() < dictT.get(c).intValue()) {
                    formed--;
                }

                l++;
            }

            r++;
        }

        return ans[0] == -1 ? "" : s.substring(ans[1], ans[2] + 1);
    }
}

var minWindow = function (s, t) {
    if (s.length === 0 || t.length === 0) {
        return "";
    }
    let dictT = new Map();
    for (let i = 0; i < t.length; i++) {
        let count = dictT.get(t.charAt(i)) || 0;
        dictT.set(t.charAt(i), count + 1);
    }
    let required = dictT.size;
    let l = 0,
        r = 0;
    let formed = 0;
    let windowCounts = new Map();
    let ans = [-1, 0, 0];
    while (r < s.length) {
        let c = s.charAt(r);
        let count = windowCounts.get(c) || 0;
        windowCounts.set(c, count + 1);
        if (dictT.has(c) && windowCounts.get(c) === dictT.get(c)) {
            formed++;
        }
        while (l <= r && formed === required) {
            c = s.charAt(l);
            if (ans[0] === -1 || r - l + 1 < ans[0]) {
                ans[0] = r - l + 1;
                ans[1] = l;
                ans[2] = r;
            }
            windowCounts.set(c, windowCounts.get(c) - 1);
            if (dictT.has(c) && windowCounts.get(c) < dictT.get(c)) {
                formed--;
            }
            l++;
        }
        r++;
    }
    return ans[0] === -1 ? "" : s.substring(ans[1], ans[2] + 1);
};

class Solution:
    def minWindow(self, s: str, t: str) -> str:
        if not t or not s:
            return ""

        dict_t = Counter(t)
        required = len(dict_t)
        l, r = 0, 0
        formed = 0
        window_counts = {}
        ans = float("inf"), None, None

        while r < len(s):
            character = s[r]
            window_counts[character] = window_counts.get(character, 0) + 1

            if character in dict_t and window_counts[character] == dict_t[character]:
                formed += 1

            while l <= r and formed == required:
                character = s[l]
                if r - l + 1 < ans[0]:
                    ans = (r - l + 1, l, r)

                window_counts[character] -= 1
                if character in dict_t and window_counts[character] < dict_t[character]:
                    formed -= 1

                l += 1

            r += 1
        return "" if ans[0] == float("inf") else s[ans[1]: ans[2] + 1]

func minWindow(s string, t string) string {
    if len(s) == 0 || len(t) == 0 {
        return ""
    }
    dictT := make(map[rune]int)
    for _, c := range t {
        dictT[c]++
    }
    required := len(dictT)
    l, r := 0, 0
    formed := 0
    windowCounts := make(map[rune]int)
    ans := []int{-1, 0, 0}
    for r < len(s) {
        c := rune(s[r])
        windowCounts[c]++
        if _, ok := dictT[c]; ok && windowCounts[c] == dictT[c] {
            formed++
        }
        for l <= r && formed == required {
            c = rune(s[l])
            if ans[0] == -1 || r-l+1 < ans[0] {
                ans[0] = r - l + 1
                ans[1] = l
                ans[2] = r
            }
            windowCounts[c]--
            if _, ok := dictT[c]; ok && windowCounts[c] < dictT[c] {
                formed--
            }
            l++
        }
        r++
    }
    if ans[0] == -1 {
        return ""
    }
    return s[ans[1] : ans[2]+1]
}

Algorithm

1️⃣

Мы начинаем с двух указателей, left и right, которые изначально указывают на первый element строки S.

2️⃣

Мы используем указатель right для расширения окна до тех пор, пока не получим желаемое окно, т.е. окно, которое содержит все символы из T.

3️⃣

Как только у нас есть окно со всеми символами, мы можем передвигать указатель left вперёд по одному. Если окно по-прежнему желаемое, мы продолжаем обновлять размер минимального окна. Если окно больше не желаемое, мы повторяем шаг 2 и далее.

😎