What's the best way in JavaScript to test if a given parameter is a square number?

问题

I created a function that will test to see if a given parameter is a square number.

Read about square numbers here: https://en.wikipedia.org/?title=Square_number

If the number is a square number, it returns true and otherwise false. Negative numbers also return false.

Examples:

isSquare(-12) // => false
isSquare( 5) // => false
isSquare( 9) // => true
isSquare(25) // => true
isSquare(27) // => false

Right now, I am using this method: http://jsfiddle.net/marcusdei/ujtc82dq/5/

But, is there a shorter more cleaner way to get the job done?

回答1:

Try this:

var isSquare = function (n) {
    return n > 0 && Math.sqrt(n) % 1 === 0;
};

1. Check if number is positive
2. Check if sqrt is complete number i.e. integer

Demo

回答2:

I would definitely go for:

var isSquare = function (n) {
    return Math.sqrt(n) % 1 === 0;
};

PS: 0 is a square number for those who wonder

Demo

回答3:

It's a bit trickier if you're using the new BigInt in JavaScript:

// integer square root function (stolen from the interwebs)
function sqrt(n) {
  let a = 1n;
  let b = (n >> 5n) + 8n;
  while (b >= a) {
    let mid = (a + b) >> 1n;
    if (mid * mid > n) {
      b = mid -= 1n;
    } else {
      a = mid += 1n;
    }
  }
  return a -= 1n;
}

sqrt(25n) === 5n
sqrt(26n) === 5n
...
sqrt(35n) === 5n

The best and fastest way I've found (so far) to determine if n is a square is:

function isSquare(n) {
   return n%sqrt(n) === 0n
}

But there's gotta be a faster way for BigInt operations.

来源：https://stackoverflow.com/questions/30919111/whats-the-best-way-in-javascript-to-test-if-a-given-parameter-is-a-square-numbe