367.有效的完全平方数.js

/*
 * @lc app=leetcode.cn id=367 lang=javascript
 *
 * [367] 有效的完全平方数
 */

// @lc code=start
/**
 * @param {number} num
 * @return {boolean}
 */
var isPerfectSquare = function(num) {
  if (num === 1) return true;

  let left = 0,
    right = num/2,
    mid = null;

  while (right >= left) {
    mid = Math.floor(left + (right - left) / 2);
    if (mid * mid === num) {
      return true;
    } else if (mid * mid > num) {
      right = mid-1;
    } else {
      left = mid+1;
    }
  }

  return false;
};
// @lc code=end