Leetcode【Sliding Window】

 

 public int lengthOfLongestSubstring(String s) {
        if (s.length() == 0){
            return 0;
        }
        HashMap<Character,Integer> map = new HashMap<>();
        int max  = 0;
        int left = 0;
        for (int i = 0; i < s.length(); i++){
            if (map.containsKey(s.charAt(i))){
                left = Math.max(left,map.get(s.charAt(i)) + 1);
            }
            map.put(s.charAt(i),i);
            max = Math.max(max,i - left + 1);
        }
        return max;
    }

    public List<String> findRepeatedDnaSequences(String s) {
        List<String> ans = new ArrayList<>();
        int n = s.length();
        Map<String, Integer> map = new HashMap<>();
        for (int i = 0; i + 10 <= n; i++) {
            String cur = s.substring(i, i + 10);
            int cnt = map.getOrDefault(cur, 0);
            if (cnt == 1) ans.add(cur);
            map.put(cur, cnt + 1);
        }
        return ans;
    }

  public int minSubArrayLen(int target, int[] nums) {
        int left = 0, right = 0;
        // 维护窗口内元素之和
        int windowSum = 0;
        int res = Integer.MAX_VALUE;

        while (right < nums.length) {
            // 扩大窗口
            windowSum += nums[right];
            right++;
            while (windowSum >= target && left < right) {
                // 已经达到 target，缩小窗口，同时更新答案
                res = Math.min(res, right - left);
                windowSum -= nums[left];
                left++;