二分的上下限初始值一定要是有意义的，不要随便给一个极小值和一个极大值

e.g. 对于 D - Minimum Width
ll = 0, r = 1e18是一个错误的范围，没有考虑单个单词的长度

正确的上下限设定应该是，下限为单个单词的最长长度，上限为所有单词的长度之和(加上中间的空格)。

#include <bits/stdc++.h>

using namespace std;

typedef long long LL;

const int N = 2e5+10;

LL n, m, l[N];

LL check(LL w)
{
    LL lines = 1;

    LL tmp = l[0];
    for(int i = 1; i < n; ++i)
    {
        if(tmp + 1 + l[i] <= w)
        {
            tmp += (1 + l[i]);
        }
        else
        {
            tmp = l[i];
            lines ++;
        }
    }
    return lines;
}

int main()
{
    cin >> n >> m;
    LL ll = 0, r = 0;
    for(int i = 0; i < n ; ++i)
    {
        cin >> l[i];
        ll = max(ll, l[i]);
        r += (l[i] + 1);
    }

    while(ll < r)
    {
        LL mid = ll + r >> 1;
        if(check(mid) <= m)r = mid;
        else ll = mid + 1;

    }

    cout << ll << endl;
    return 0;
}