367 Valid Perfect Square
367. Valid Perfect Square
1. Question
Given a positive integernum, write a function which returns True ifnumis a perfect square else False.
Note:Do not use any built-in library function such assqrt
.
Example 1:
Input: 16
Returns: True
Example 2:
Input: 14
Returns: False
2. Implementation
(1) Binary Search
class Solution {
public boolean isPerfectSquare(int num) {
if (num < 1) {
return false;
}
long start = 1, end = num, mid = 0;
while (start + 1 < end) {
mid = start + (end - start) / 2;
if (mid * mid == num) {
return true;
}
else if (mid * mid < num) {
start = mid + 1;
}
else {
end = mid - 1;
}
}
if (start * start == num || end * end == num) {
return true;
}
else {
return false;
}
}
}
3. Time & Space Complexity
Binary Search: 时间复杂度O(logn), 空间复杂度O(1)
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