[leetCode]209. 长度最小的子数组

双指针

class Solution {
    public int minSubArrayLen(int s, int[] nums) {
        if (nums.length == 0)
            return 0;
        int ans = Integer.MAX_VALUE;
        int start = 0, end = 0;
        int sum = 0;
        while (end < nums.length) {
            sum += nums[end];
            while (sum >= s) {
                ans = Math.min(ans, end - start + 1);
                sum -= nums[start];
                start++;
            }
            end++;
        }
        return ans == Integer.MAX_VALUE ? 0 : ans;
    }
}

前缀和 + 二分查找

class Solution {
    public int minSubArrayLen(int s, int[] nums) {
        if (nums.length == 0)
            return 0;
        int ans = Integer.MAX_VALUE;
        // 计算前缀和
        int[] sum = new int[nums.length + 1];
        for (int i = 1; i <= nums.length; i++) {
            sum[i] = sum[i-1] + nums[i - 1];
        }
        for (int i = 1; i <= nums.length; i++) {
            int target = s + sum[i-1];
            int bound = Arrays.binarySearch(sum, target);
            if (bound < 0) {
                bound = -bound -1;
            }
            if (bound <= nums.length) {
                ans = Math.min(ans, bound - (i - 1));
            }
        }
        return ans == Integer.MAX_VALUE ? 0 : ans;
    }
}