May 17, 2019

Valid Perfect Square

Given a positive integer num, write a function which returns True if num is a perfect square else False.

Note: Do not use any built-in library function such as sqrt.

Example 1:

``````Input: 16
Output: true
``````

Example 2:

``````Input: 14
Output: false
``````

Solution

``````/**
* @param {number} num
* @return {boolean}
* @time complexity: O(log n)
* @space complexity: O(1)
*/
function isValidPerfectSquare(num) {
// Binary Search
let left = 0;
let right = num;

while (left <= right) {
const mid = Math.floor((left + right) / 2);
const tmp = mid * mid;

if (tmp === num) {
return true;
}

if (tmp > num) {
right = mid - 1;
} else {
left = mid + 1;
}
}
return false;
};
``````

Test Case

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

describe('Valid Perfect Square', () => {

it('should return true when 16 is given', () => {
assert.deepEqual(isValidPerfectSquare(16), true);
});

it('should return false when 14 is given', () => {
assert.deepEqual(isValidPerfectSquare(14), false);
});

});
``````
``````  Valid Perfect Square
✓ should return true when 16 is given
✓ should return false when 14 is given

2 passing (17ms)
``````