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O(n) time and O(n) space using hashmap.

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Lines changed: 8 additions & 16 deletions

Original file line number	Diff line number	Diff line change
`@@ -22,20 +22,12 @@`
`22`	`22`	`"""`
`23`	`23`	`class Solution:`
`24`	`24`	`def checkSubarraySum(self, nums: List[int], k: int) -> bool:`
`25`		`- """`
`26`		`- The idea here is if two sums have the same module and they are atleast two indexes apart then we can return true otherwise false.`
`27`		`- For [0,2], k=2 prefix sum would be [0,2] and sum2 = 2 and sum1 = 0. sum2 - sum1 can be divided by k and the distance between those two indexes is atleast 2.`
`28`		`- """`
`29`		`- hmap = {0:-1} # initially at index -1 the sum would be zero.`
`30`		`- for i in range(1,len(nums)):`
`31`		`- nums[i] += nums[i-1] # prefix sum`
`32`		`- for i in range(len(nums)):`
`33`		`- temp = nums[i]`
`34`		`- if k:`
`35`		`- temp %= k`
`36`		`- if temp in hmap.keys():`
`37`		`- if i - hmap[temp] >= 2:`
`38`		`- return True`
	`25`	`+ hmap,total = {},0`
	`26`	`+ for i,num in enumerate(nums):`
	`27`	`+ total = (total + num) % k`
	`28`	`+ if total == 0 and i > 0: return True # if total % k =0 that means we have a multiple of k present already and check if the array size is greater than or equal to 2.`
	`29`	`+ if total not in hmap:`
	`30`	`+ hmap[total] = i`
`39`	`31`	`else:`
`40`		`- hmap[temp] =i`
`41`		`- return False`
	`32`	`+ ifi-hmap[total] >=2: returnTrue`
	`33`	`+ return False`

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