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[Leetcode] 560. 和为 K 的子数组

言午栩 2022-04-08 阅读 79
javaleetcode

给你一个整数数组 nums 和一个整数 k ,请你统计并返回 该数组中和为 k 的子数组的个数 。

示例 1:

输入:nums = [1,1,1], k = 2
输出:2
示例 2:

输入:nums = [1,2,3], k = 3
输出:2
 

提示:

1 <= nums.length <= 2 * 104
-1000 <= nums[i] <= 1000
-107 <= k <= 107

code:


public class SubarraySum {

    // 560. 和为 K 的子数组
    public int subarraySum(int[] nums, int k) {
        int count = 0, pre = 0;
        HashMap<Integer, Integer> mp = new HashMap<>();
        mp.put(0, 1);
        for (int num : nums) {
            pre += num;
            if (mp.containsKey(pre - k))
                count += mp.get(pre - k);
            mp.put(pre, mp.getOrDefault(pre, 0) + 1);
        }
        return count;
    }


    public int subarraySum1(int[] nums, int k) {
        int n = nums.length;
        int[] sum = new int[n];
        sum[0] = nums[0];
        for (int i = 1; i < n; i++) {
            sum[i] = sum[i - 1] + nums[i];
        }

        int ans = 0;
        for (int i = 0; i < n; i++) {
            if (sum[i] == k) {
                ans++;
            }
            for (int j = 0; j < i; j++) {
                if (sum[i] - sum[j] == k) {
                    ans++;
                }
            }
        }
        return ans;
    }

    public static void main(String[] args) {

        SubarraySum solution = new SubarraySum();
        int[] nums = new int[]{1, 1, 1};
        System.out.println(solution.subarraySum(nums, 2));

    }
}
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