滑动窗口的解题思路

题一：无重复字符的最长子串

class Solution {
    public int lengthOfLongestSubstring(String s) {
        if (s.length()==0) return 0;
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();
        int max = 0;
        int left = 0;
        for(int i = 0; i < s.length(); i ++){
            // 如果已经存在当前元素，移动左窗口的值
            if(map.containsKey(s.charAt(i))){
                left = Math.max(left,map.get(s.charAt(i)) + 1);
            }
            // 更新索引值
            map.put(s.charAt(i),i);
            max = Math.max(max,i-left+1);
        }
        return max;

    }
}

题二：长度最小的子数组

class Solution {
    public int minSubArrayLen(int s, int[] nums) {
        int i = 0;
        int sum = 0;
        int len = 0;
        for (int j = 0; j < nums.length; j++) {
            sum += nums[j];
            while (sum >= s) {
                len = len == 0 ? j - i + 1 : Math.min(len, j - i + 1);
                sum -= nums[i++];
            }
        }
        return len;
    }
}