Poison

367. Valid Perfect Square

发表于 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
class Solution {
    public boolean isPerfectSquare(int num) {
        int left = 1, right = num;
        int ans = 0;
        while (left <= right) {
            int mid = (left + right) >>> 1;
            if (mid <= num / mid) {
                ans = mid;
                left = mid + 1;
            } else {
                right = mid - 1;
            }
        }

        return ans * ans == num;
    }
}
Math
1
2
3
4
5
6
7
8
9
10
11
class Solution {
    public boolean isPerfectSquare(int num) {
        int x = 1;
        while (num > 0) {
            num -= x;
            x += 2;
        }

        return num == 0;
    }
}
Reference

367. Valid Perfect Square