UVA-714 二分

        把可能的进行二分判断，判断的时候尽量向右取，一直取到不能去为止，这样才有可能成功分割。

判断是否可以把up作为最大值的代码：

bool judge(LL up){if(up < Big) return false; //Big是数组中最大值，如果up小于最大值是不可能成功划分的LL sum = 0;int cnt = 0;for(int i = 0; i < n; ){sum = 0;while(i < n){sum += a[i];if(sum <= up) ++i;else break;}++cnt;}if(cnt <= k) return true; //成功划分return false;
}

值得注意的是，最后得到最小的最大值时应该如何划分，题目要求前面的尽量小，那么就从后面尽可能多的划分，但是不能只满足小于等于up，也要考虑到组成k个序列，不能让某些序列为空。

AC代码：

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
typedef long long LL;
const int maxn = 500 + 5;
int a[maxn], vis[maxn];
int Big = -1; //Biggest number
int n,k; //Divid n numbers to k squencesbool judge(LL up){if(up < Big) return false;LL sum = 0;int cnt = 0;for(int i = 0; i < n; ){sum = 0;while(i < n){sum += a[i];if(sum <= up) ++i;else break;}++cnt;}if(cnt <= k) return true;return false;
}LL Binary_Search(LL x, LL y){ //[x,y]while(x < y){LL mid = x + (y - x) / 2;bool ok = judge(mid);if(ok) y = mid;else x = mid + 1;}return y;
}int main(){int T;scanf("%d", &T);while(T--) {memset(vis, 0, sizeof(vis));LL sum = 0;Big = -1;scanf("%d%d",&n,&k);for(int i = 0; i < n; ++i){scanf("%d",&a[i]);sum += a[i];Big = max(Big, a[i]);}LL up = Binary_Search(1, sum);LL div;int cnt = 0;for( int  i = n-1; i >= 0;){div = 0;while(div <= up && i >= 0 && i + 1 >= k - cnt){div += a[i];if(div <= up) --i;}++cnt;if(i >= 0) vis[i] = 1;}//print the answerfor(int i = 0; i < n; ++i){if(i == n-1) printf("%d\n", a[i]);else printf("%d ", a[i]);if(vis[i]) printf("/ ");}}return 0;
}

如有不当之处欢迎指出！