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
一刷
解法： binarySearch。
class Solution {
public boolean isPerfectSquare(int num) {
int low = 1, high = num;
while (low <= high) {
long mid = (low + high) >>> 1;
if (mid * mid == num) {
return true;
} else if (mid * mid < num) {
low = (int) mid + 1;
} else {
high = (int) mid - 1;
}
}
return false;
}
}
