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 分析：
二分。注意溢出！
public class Solution {
public boolean isPerfectSquare(int num) {
long begin = ;
long end = num;
while (begin <= end) {
long mid = (end + begin) / ;
if (mid * mid == num) {
return true;
} else if (mid * mid < num) {
begin = mid + ;
} else {
end = mid - ;
}
}
return false;
}
}