Good morning! Here's our prompt for today.

Given an array of numbers, return true if there is a subarray that sums up to a certain number n.

A subarray is a contiguous subset of the array. For example the subarray of [1,2,3,4,5] is [1,2,3] or [3,4,5] or [2,3,4] etc.

1const arr = [1, 2, 3], sum = 5
2subarraySum(arr, sum)
3// true
4// [2, 3] sum up to 5
5
6const arr = [11, 21, 4], sum = 9
7subarraySum(arr, sum)
8// false
9// no subarrays sums up to 9

In the above examples, [2, 3] sum up to 5 so we return true. On the other hand, no subarray in [11, 21, 4] can sum up to 9.

Can you create a function subarraySum that accomplishes this?

Constraints

• Length of the array <= 100000
• The values in the array will be between 0 and 1000000000
• The target sum n will be between 0 and 1000000000
• The array can be empty
• Expected time complexity : O(n)
• Expected space complexity : O(n)

Try to solve this here or in Interactive Mode.

How do I practice this challenge?

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var assert = require('assert');

​

function subarraySum(nums, n) {

  // hash of prefix sums

​

  // Fill in this method

  return nums;

}

​

const arr = [1, 2, 3],

  sum = 5;

console.log(subarraySum(arr, sum));

​

try {

  assert.equal(subarraySum([1, 2, 3], 3), true);

​

  console.log('PASSED: ' + 'assert.equal(subarraySum([ 1, 2, 3 ], 3), true)');

} catch (err) {

  console.log(err);

}

​

try {

  assert.equal(subarraySum([], 3), false);

​

  console.log('PASSED: ' + 'assert.equal(subarraySum([], 3), false)');

} catch (err) {

  console.log(err);

}

​

Here's a video of us explaining the solution.

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Here's our guided, illustrated walk-through.

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