Not 67 days, square root

class Solution {
    public int mySqrt(int x) {
        int l = 0, r = x, ans = -1;
        while (l <= r) {
            int mid = l + (r - l) / 2;
            if ((long) mid * mid <= x) {
                ans = mid;
                l = mid + 1;
            } else {
                r = mid - 1;
            }
        }
        return ans;
    }
}

 author ：LeetCode-Solution
 link ：https://leetcode.cn/problems/jJ0w9p/solution/qiu-ping-fang-gen-by-leetcode-solution-ybnw/
 source ： Power button （LeetCode）
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