367. 有效的完全平方数(java)

二分法：

class Solution {
    public boolean isPerfectSquare(int num) {
      int left = 0,right = num;
      if(num==1)
      {
          return true;
      }
      while(left
          int mid = ((right-left)/2)+left;
          long x = (long)mid*mid;
          if(num
              right=mid;
          }else if(num>x)
            {
                left=mid+1;
            }else
            {
                return true;
            }
      }
      return false;

    }
}

暴力解法：

int n = 1;
	while (num / n >= n) {
		if (num % n==0 && num/n == n) {
			return true;
		}
		n++;
	}
	return false;

牛顿迭代：

class Solution {
    public boolean isPerfectSquare(int num) {
        double x = num;
        while(x * x - num > 0.00000001){
            x = (num/x + x)/2;
        }
        int y = (int)x;
        return y*y == num;
    }
}