Solution.java

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);
    }
}