367 Valid Perfect Square
Problem:
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
Solutions:
public class Solution {
public boolean isPerfectSquare(int num) {
for (int i = 0; i * i >= 0 && i * i <= num; i ++) {
if (i * i == num) {
return true;
}
}
return false;
}
}
public class Solution {
public boolean isPerfectSquare(int num) {
int i = 1;
while (num > 0) {
num -= i;
i += 2;
}
return num == 0;
}
}
public class Solution {
public boolean isPerfectSquare(int num) {
long left = 0, right = num;
while (left <= right) {
long mid = left + (right - left) / 2, t = mid * mid;
if (t == num) return true;
else if (t < num) left = mid + 1;
else right = mid - 1;
}
return false;
}
}