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leetcode 76. minimum window substring

admin 11月 13, 2020 0

76. Minimum Window Substring

Difficulty:: Hard

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).

Example:

1 2	Input: S = "ADOBECODEBANC", T = "ABC" Output: "BANC"

Note:

If there is no such window in S that covers all characters in T, return the empty string "".
If there is such window, you are guaranteed that there will always be only one unique minimum window in S.

Solution

Language: Java

class  {
    public String minWindow(String s, String t) {
        if (s == null || s.length() == 0 || t == null || t.length() == 0) {
            return "";
        }
        int[] targetMap = new int[256];
        int[] sourceMap = new int[256];
        for (int i = 0; i < t.length(); i++) {
            targetMap[t.charAt(i)]++;
        }
        int min = Integer.MAX_VALUE;
        String minString = "";
        for (int i = 0, j = 0; i < s.length(); i++) {
            while (j < s.length() && !isValid(sourceMap, targetMap)) {
                sourceMap[s.charAt(j)]++;
                j++;
            }
            if (min > j - i && isValid(sourceMap, targetMap)) {
                minString = s.substring(i, j);
                min = j - i;
            }
            sourceMap[s.charAt(i)]--;
        }
        return minString;
    }
    
    private boolean isValid(int[] source, int[] target) {
        for (int i = 0; i < target.length; i++) {
            if (target[i] > source[i]) {
                return false;
            }
        }
        return true;
    }
}