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Given an array of integers and an integer k, you need to find the total number of continuous subarrays whose sum equals to k.
Example 1:
Input:nums = [1,1,1], k = 2 Output: 2
Note:
- The length of the array is in range [1, 20,000].
- The range of numbers in the array is [-1000, 1000] and the range of the integer k is [-1e7, 1e7].
解题思路:利用HashMap
class Solution {
public int subarraySum(int[] nums, int k) {
int count = 0,sum = 0;
Map<Integer,Integer> map = new HashMap<>();
map.put(0,1);
for(int i = 0;i<nums.length;i++) {
sum += nums[i];
if(map.containsKey(sum - k)) {
count += map.get(sum - k);
}
if(map.containsKey(sum)) {
map.put(sum,map.get(sum) + 1);
}
else
{
map.put(sum,1);
}
}
return count;
}
}
tips:map的key存储子序列的和,当出现关键字已经存在的子序列时,需要获得该关键字的值再加一的原因是:此时的子序列可以选择与之前出现的子序列和为k的子序列组合,也可以不组合。,