public class Solution { public boolean isPerfectSquare(int num) { long lo = 1, hi = num / 2; if(num == 1) return true; long x = num; while(lo <= hi) { long mid = lo + (hi - lo) / 2; if(mid * mid == x) return true; else if(mid * mid < x) lo = mid + 1; else hi = mid - 1; } return false; } }