Question
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
Code
public class Solution {
public boolean isPerfectSquare(int num) {
if (num == 0 || num == 1) return true;
if (num < 0) return false;
long l = 0L, h = (long) num, temp = (long) num;
while (l <= h) {
if (l + 1 == h) {
if (temp > l * l && temp < h * h) return false;
}
long mid = l + (h - l) / 2;
if (temp == mid * mid) return true;
if (temp < mid * mid) {
h = mid - 1;
} else {
l = mid + 1;
}
}
return false;
}
}
Solution
使用二分查找法。注意使用long来代替int进行计算，否则会因为溢出而出错。
