重启——二分

整数二分

    while (m -- )
    {
        int x;
        scanf("%d", &x);

        int l = 0, r = n - 1;
        while (l < r)//模板一
        {
            int mid = l + r >> 1;
            if (q[mid] >= x) r = mid;
            else l = mid + 1;
        }

        if (q[l] != x) cout << "-1 -1" << endl;
        else
        {
            cout << l << ' ';

            int l = 0, r = n - 1;
            while (l < r)//模板二
            {
                int mid = l + r + 1 >> 1;
                if (q[mid] <= x) l = mid;
                else r = mid - 1;
            }

            cout << l << endl;
        }
    }

浮点数二分

	while(r-l>1e-6) //－几比结果需要的精度多两位，如保留4位，则r-l>1e-6
	{
		double mid = l+r >>1;
		if(mid*mid>=x) r=mid;
		else l = mid; 
	}
	原理：区间长度极小时可视为一个数字