数列分段

ybtoj 二分-1-1

题目大意

给出一个序列A，让你把它分成m段，使每段和最大值最小

输入样例

5 3
4 2 4 5 1

输出样例

6

数据范围

$1⩽M⩽N⩽10^5$
$sum\left\{\begin{array}{c}{A}_i\end{array}\right\}⩽10^9$

解题思路

二分枚举答案
然后$O(n)$判断

代码

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define ll long long
using namespace std;
ll n, m, l, r, mid, a[100010];
bool check(ll x)//判断
{ll g = 0, gg = 1;for (int i = 1; i <= n; ++i)if (g + a[i] <= x) g += a[i];else g = a[i], gg++;//新的一段return gg <= m;
}
int main()
{scanf("%lld%lld", &n, &m);for (int i = 1; i <= n; ++i){scanf("%lld", &a[i]);l = max(l, a[i]);r += a[i];} while(l < r)//二分{mid = (l + r)>>1;if (check(mid)) r = mid;else l = mid + 1;}printf("%lld", l);return 0;
}