LeetCode 76. 最小覆盖子串

76. 最小覆盖子串

解题思路

参考代码

class Solution {
    public String minWindow(String s, String t) {
        if(s.length() == 0 || t.length() == 0) {
            return "";
        }
        // 记录 t 中每个字符出现的次数
        Map<Character, Integer> mapT = new HashMap<>();
        // 记录窗口中每个字符出现的次数
        Map<Character, Integer> mapW = new HashMap<>();
        for(int i = 0; i < t.length(); i ++) {
            char ch = t.charAt(i);
            mapT.put(ch, mapT.getOrDefault(ch, 0) + 1);
        }
        int tCount = mapT.size();
        int resStart = 0, resLen = Integer.MAX_VALUE;
        int left = 0, right = 0;
        while(right < s.length()) {
            char rightChar = s.charAt(right);
            mapW.put(rightChar, mapW.getOrDefault(rightChar, 0) + 1);

            // 如果窗口中包含了 t 中的所有字符，尝试缩小窗口
            while(isFullInclude(mapT, mapW)) {
                int windowLen = right - left + 1;
                // 如果当前窗口长度小于之前记录的最小长度，更新窗口起始位置和最小长度
                if(windowLen < resLen) {
                    resLen = windowLen;
                    resStart = left;
                }

                char leftChar = s.charAt(left);
                mapW.put(leftChar, mapW.get(leftChar) - 1);
                left ++;
            }
            right ++;
        }
        if(resLen == Integer.MAX_VALUE) return "";
        return s.substring(resStart, resStart + resLen);
    }
    /**
     * 判断窗口中是否包含了 t 中的所有字符
     */
    private static boolean isFullInclude(Map<Character, Integer> mapT, Map<Character, Integer> mapW) {
        for(Map.Entry<Character, Integer> key : mapT.entrySet()) {
            char c = key.getKey();
            int valueT = key.getValue();
            if(mapW.containsKey(c)) {
                int valueW = mapW.get(c);
                if(valueT > valueW) {
                    return false;
                }
            } else {
                return false;
            }
        }
        return true;
    }
}