Leetcode 367. Valid Perfect Square[medium]

题目：

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

Credits:

Special thanks to @elmirap for adding this problem and creating all test cases.

水题。二分法求根。

class Solution {
public:
bool isPerfectSquare(int num) {
//0-46340
int l = 0, r = 46340;
int mid, midx;
while (l <= r) {
mid = l + r >> 1;
midx = mid * mid;
if (midx == num) return true;
else if (midx < num) l = mid + 1;
else r = mid - 1;
}
return false;
}
};