Given an array of integers nums and an integer k, return the total number of continuous subarrays whose sum equals to k.
Example 1:
Input: nums = [1,1,1], k = 2 Output: 2
Example 2:
Input: nums = [1,2,3], k = 3 Output: 2
Constraints:
1 <= nums.length <= 2 * 104-1000 <= nums[i] <= 1000-107 <= k <= 107、
class Solution {
public int subarraySum(int[] nums, int k) {
int count=0;
int[] arr = new int[nums.length+1];
arr[0]=0;
for(int i=1;i<arr.length;i++){
arr[i]=arr[i-1]+nums[i-1];
}
for(int i=0;i<arr.length-1;i++){
for(int j=i+1;j<arr.length;j++){
if(arr[j]-arr[i]==k) count++;
}
}
return count;
}
}
class Solution {
public int subarraySum(int[] nums, int k) {
int count=0;
int[] arr = new int[nums.length+1];
arr[0]=0;
for(int i=1;i<arr.length;i++){
arr[i]=arr[i-1]+nums[i-1];
}
Map<Integer,Integer> map = new HashMap();
for(int i=0;i<arr.length;i++){
count+=map.getOrDefault(arr[i]-k,0);
map.put(arr[i],map.getOrDefault(arr[i],0)+1);
}
return count;
}
}
560. Subarray Sum Equals K Medium
Given an array of integers nums and an integer k, return the total number of continuous subarrays whose sum equals to k.
Example 1:
Input: nums = [1,1,1], k = 2 Output: 2
Example 2:
Input: nums = [1,2,3], k = 3 Output: 2
Constraints:
1 <= nums.length <= 2 * 104-1000 <= nums[i] <= 1000-107 <= k <= 107
class Solution {
public int subarraysDivByK(int[] nums, int k) {
Map<Integer,Integer> map = new HashMap();
int count = 0;
int sum=0;
map.put(0,1);
for(int i=0;i<nums.length;i++){
sum=(sum+nums[i]%k+k)%k;//这里加k是为了防止负数
count += map.getOrDefault(sum,0);
map.put(sum,map.getOrDefault(sum,0)+1);
}
return count;
}
}