May 27, 2019

# Minimum Size Subarray Sum

Given an array of n positive integers and a positive integer s, find the minimal length of a contiguous subarray of which the sum ≥ s. If there isn't one, return 0 instead.

Example:

``````Input: s = 7, nums = [2,3,1,2,4,3]
Output: 2
Explanation: the subarray [4,3] has the minimal length under the problem constraint.
``````

### Solution

``````/**
* @param {number} s
* @param {number[]} nums
* @return {number}
* @time complexity: O(n)
* @space complexity: O(1)
*/
var minSubArrayLen = function(s, nums) {
let res = Infinity;
let sum = 0;
let i = 0;

for (let j = 0; j < nums.length; j++) {
sum += nums[j];

while (sum >= s) {
res = Math.min(res, j - i + 1);
sum -= nums[i];
i++;
}
}

return res === Infinity ? 0 : res;
};
``````

### Test Case

``````const assert = require('chai').assert;

describe('Minimum Size Subarray Sum', () => {

it('should return the minimal length', () => {
assert.strictEqual(minSubArrayLen(7, [2, 3, 1, 2, 4, 3]), 2);
});

it('should return 0 when there isn\' one', () => {
assert.strictEqual(minSubArrayLen(30, [2, 3, 1, 2, 4, 3]), 0);
});

});
``````
``````  Minimum Size Subarray Sum
✓ should return the minimal length
✓ should return 0 when there isn' one

2 passing (12ms)
``````