题解 | #最小覆盖子串#

public class Solution {
    /**
     * 
     * @param S string字符串 
     * @param T string字符串 
     * @return string字符串
     */
    public String minWindow (String S, String T) {
        // write code here
        if (S == null || S.length() < 1 || T == null || T.length() < 1) {
            return "";
        }
        char[] sArr = S.toCharArray();
        char[] tArr = T.toCharArray();
        int[] map = new int[128];
        for (char ch : tArr) {
            map[(int) ch]++;
        }
        int slow = 0;
        int fast = 0;
        int left = -1;
        int right = -1;
        int cnt = tArr.length;
        int len = Integer.MAX_VALUE;
        while (fast < sArr.length) {
            char ch = sArr[fast];
            int key = (int) ch;
            if (map[key]-- > 0) {
                cnt--;
            }
            while (cnt == 0) {
                if (fast - slow + 1 < len) {
                    len = fast - slow + 1;
                    left = slow;
                    right = fast;
                }
                ch = sArr[slow];
                key = (int) ch;
                if (map[key]++ == 0) {
                    cnt++;
                }
                slow++;
            }
            fast++;
        }
        if (left == -1) {
            return "";
        }
        return S.substring(left, right + 1);
    }
    
}