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));
}
}