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.
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思路：
二分查找。
java code:
public class Solution {
public boolean isPerfectSquare(int num) {
long lo = 1, hi = num / 2;
if(num == 1) return true;
long x = num;
while(lo <= hi) {
long mid = lo + (hi - lo) / 2;
if(mid * mid == x)
return true;
else if(mid * mid < x)
lo = mid + 1;
else
hi = mid - 1;
}
return false;
}
}原文：http://blog.csdn.net/itismelzp/article/details/51773849