367. 检验完全平方数 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
Returns: True

Example 2:

Input: 14
Returns: False

题意：给一个非负的整形，判断它是否为完全平方数

解法：使用二分法搜索，右界从num/2开始。还要注意数据类型溢出的问题

public class Solution {
    public bool IsPerfectSquare(int num) {
		long l = 1, r = num/2 + 1;
		while (l <= r) {
			long m = l + (r - l) / 2;
			long pow = m * m;
			if (pow == num) {
				return true;
			} else if (pow > num) {
				r = m - 1;
			} else if (pow < num) {
				l = m + 1;
			}
		}
		return false;
    }
}

null