#0290

Subarray Sum Equals K

MediumDSA28 min20 XP

Problem

Given nums and k, return the number of contiguous subarrays with sum exactly k.

Why This Matters

Prefix-sum counting is the key pattern when negative numbers make sliding windows invalid.

Function Signature

def subarray_sum(nums, k):

Examples

Example 1

Inputnums = [1,1,1], k = 2

Output2

The first two and last two elements both sum to 2.

Constraints

Return the exact requested value.
Handle edge cases cleanly.
Use the intended DSA pattern when brute force would scale poorly.

CodePython

def subarray_sum(nums, k):
    """
    Input example: nums = [1,1,1], k = 2
    Return: 2
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return 0

def subarray_sum(nums, k):
    """
    Input example: nums = [1,1,1], k = 2
    Return: 2
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return 0

Visible browser tests run here when available.

Testcases2 visible / 3 hidden categories

Two subarrays

Input[1,1,1], k = 2

Expected2

There are two length-2 windows.

Negative values

Input[1,-1,0], k = 0

Expected3

[1,-1], [1,-1,0], and [0] all sum to zero.

Hidden Test Categories

empty inputall zerostarget negative