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Copy path560_Subarray_Sum_Equals_K.swift
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40 lines (37 loc) · 1.05 KB
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import Foundation
// Time: O(n^2)
class Solution {
func subarraySum(_ nums: [Int], _ k: Int) -> Int {
var prefixSum = [Int]()
prefixSum.append(0)
for num in nums {
prefixSum.append(prefixSum.last! + num)
}
var count = 0
for i in 0..<nums.count {
for j in i..<nums.count {
if prefixSum[j + 1] - prefixSum[i] == k {
count += 1
}
}
}
return count
}
}
// Time: O(n)
import Foundation
class Solution {
func subarraySum(_ nums: [Int], _ k: Int) -> Int {
var prefixSumCounterMap = [Int:Int](), totalCount = 0, currentSum = 0
prefixSumCounterMap[0] = 1
for num in nums {
currentSum += num
let prevPrefixSum = currentSum - k
if let currentCount = prefixSumCounterMap[prevPrefixSum] {
totalCount += currentCount
}
prefixSumCounterMap[currentSum, default: 0] += 1
}
return totalCount
}
}