367. 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
Example 1:
Note: Do not use any built-in library function such as
sqrt.Example 1:
Input: 16 Output: true
Example 2:
Input: 14 Output: false
思路：给定一个正整数，判断该数字是否能开平方根，且根为整数。题目要求不能用内置方法sqrt。二分查找法。
代码如下：
public static boolean isPerfectSquare(int num) {
if (num == 1) return true;
int start = 1;
int end = num;
while (start <= end){
int mid = start + (end - start) / 2;
if (mid * mid == num){
return true;
}else if (mid * mid < num){
start = mid + 1;
}else if (mid * mid > num){
end = mid - 1;
}
}
return false;
}
