# 727. Minimum Window Subsequence

## Description

Given strings s1 and s2, return the minimum contiguous substring part of s1, so that s2 is a subsequence of the part.

If there is no such window in s1 that covers all characters in s2, return the empty string "". If there are multiple such minimum-length windows, return the one with the left-most starting index.

Example 1:

Input: s1 = "abcdebdde", s2 = "bde"
Output: "bcde"
Explanation:
"bcde" is the answer because it occurs before "bdde" which has the same length.
"deb" is not a smaller window because the elements of s2 in the window must occur in order.


Example 2:

Input: s1 = "jmeqksfrsdcmsiwvaovztaqenprpvnbstl", s2 = "u"
Output: ""


Constraints:

• 1 <= s1.length <= 2 * 104
• 1 <= s2.length <= 100
• s1 and s2 consist of lowercase English letters.

## Solutions

• class Solution {
public String minWindow(String s1, String s2) {
int m = s1.length(), n = s2.length();
int[][] f = new int[m + 1][n + 1];
for (int i = 1; i <= m; ++i) {
for (int j = 1; j <= n; ++j) {
if (s1.charAt(i - 1) == s2.charAt(j - 1)) {
f[i][j] = j == 1 ? i : f[i - 1][j - 1];
} else {
f[i][j] = f[i - 1][j];
}
}
}
int p = 0, k = m + 1;
for (int i = 1; i <= m; ++i) {
if (s1.charAt(i - 1) == s2.charAt(n - 1) && f[i][n] > 0) {
int j = f[i][n] - 1;
if (i - j < k) {
k = i - j;
p = j;
}
}
}
return k > m ? "" : s1.substring(p, p + k);
}
}

• class Solution {
public:
string minWindow(string s1, string s2) {
int m = s1.size(), n = s2.size();
int f[m + 1][n + 1];
memset(f, 0, sizeof(f));
for (int i = 1; i <= m; ++i) {
for (int j = 1; j <= n; ++j) {
if (s1[i - 1] == s2[j - 1]) {
f[i][j] = j == 1 ? i : f[i - 1][j - 1];
} else {
f[i][j] = f[i - 1][j];
}
}
}
int p = 0, k = m + 1;
for (int i = 1; i <= m; ++i) {
if (s1[i - 1] == s2[n - 1] && f[i][n]) {
int j = f[i][n] - 1;
if (i - j < k) {
k = i - j;
p = j;
}
}
}
return k > m ? "" : s1.substr(p, k);
}
};

• class Solution:
def minWindow(self, s1: str, s2: str) -> str:
m, n = len(s1), len(s2)
f = [[0] * (n + 1) for _ in range(m + 1)]
for i, a in enumerate(s1, 1):
for j, b in enumerate(s2, 1):
if a == b:
f[i][j] = i if j == 1 else f[i - 1][j - 1]
else:
f[i][j] = f[i - 1][j]
p, k = 0, m + 1
for i, a in enumerate(s1, 1):
if a == s2[n - 1] and f[i][n]:
j = f[i][n] - 1
if i - j < k:
k = i - j
p = j
return "" if k > m else s1[p : p + k]


• func minWindow(s1 string, s2 string) string {
m, n := len(s1), len(s2)
f := make([][]int, m+1)
for i := range f {
f[i] = make([]int, n+1)
}
for i := 1; i <= m; i++ {
for j := 1; j <= n; j++ {
if s1[i-1] == s2[j-1] {
if j == 1 {
f[i][j] = i
} else {
f[i][j] = f[i-1][j-1]
}
} else {
f[i][j] = f[i-1][j]
}
}
}
p, k := 0, m+1
for i := 1; i <= m; i++ {
if s1[i-1] == s2[n-1] && f[i][n] > 0 {
j := f[i][n] - 1
if i-j < k {
k = i - j
p = j
}
}
}
if k > m {
return ""
}
return s1[p : p+k]
}

• function minWindow(s1: string, s2: string): string {
const m = s1.length;
const n = s2.length;
const f: number[][] = Array(m + 1)
.fill(0)
.map(() => Array(n + 1).fill(0));
for (let i = 1; i <= m; ++i) {
for (let j = 1; j <= n; ++j) {
if (s1[i - 1] === s2[j - 1]) {
f[i][j] = j === 1 ? i : f[i - 1][j - 1];
} else {
f[i][j] = f[i - 1][j];
}
}
}
let p = 0;
let k = m + 1;
for (let i = 1; i <= m; ++i) {
if (s1[i - 1] === s2[n - 1] && f[i][n]) {
const j = f[i][n] - 1;
if (i - j < k) {
k = i - j;
p = j;
}
}
}
return k > m ? '' : s1.slice(p, p + k);
}