二分写法

二分的正确写法

整数二分

int l = 0, r = n;
while (l <= r) {
    int nMid = (l + r) >> 1;
    if (Judge(x, y, nMid)) {
        l = nMid + 1;
    }
    else {
        r = nMid - 1;
    }
}

//注意当l为0时, 输出0, 而非-1
cout << l - 1 << endl;

实数二分

double l = 0, r = n;
//精度具体看题意
while (r - l > 0.0001) {
    double nMid = (l + r) / 2.0;
    if (Judge(x, y, nMid)) {
        l = nMid;
    }
    else {
        r = nMid;
    }
}

cout << l << endl;