69. x 的平方根（二分）

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