Valid Perfect Square Problem & Solution
Given a positive integer num, write a function which returns True if num is a perfect square else False.
Do not use any built-in library function such as sqrt.
See the valid perfect square problem on LeetCode.
C++ Solution
#pragma GCC optimize("Ofast")
#pragma GCC optimization("unroll-loops")
static const int _=[](){std::ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);return 0;}();
class Solution {
public:
bool isPerfectSquare(int num) {
int low = 0;
int high = num;
while (low < high) {
int mid = low + (high - low) / 2;
// Avoids computing `mid * mid < num` because it overflows.
if (mid == 0 || mid < num / mid) {
low = mid + 1;
} else {
high = mid;
}
}
// Must do a float comparison rather than int to avoid rounding errors.
return low != 0 && low == (float)num / low;
}
};