二分法模板集合

二分查找

find_x(a[], x)
{
	left = 0, right = a.length - 1;
    while left <= right
        mid = (left + right) / 2;
        if a[mid] == x
            return mid;
        else if a[mid] < x
            left = mid + 1;
        else
            right = mid - 1;
    return NOT_FOUND ;
}

核心

mid = (left + right) / 2;
left = mid + 1;
right = mid - 1;

二分答案

bool check(int x) {
    int now = 0, cnt = 0;
    for (int i = 0; i < n; ++i) {
        if (now + a[i] > x) {
            ++cnt;
            now = a[i];
        } else {
            now += a[i];
        }
    }
    return cnt <= k;
}

int cal(int l, int r) {
    while (l < r) {
        int mid = (l+)) >> 1;
        if (check(mid)) {
            r = mid;
        } else {
            l = mid + 1;
        }
    }
    return l;
}

核心

mid = (l + r) >> 1;
r = mid;
l = mid + 1;