Bin Packing pku 2782

 

Bin Packing
Time Limit:2000MS  Memory Limit:65536K
Total Submit:2047 Accepted:970

Description
A set of n 1-dimensional items have to be packed in identical bins. All bins have exactly the same length l and each item i has length li<=l . We look for a minimal number of bins q such that

 

Input
The first line of the input contains the number of items n (1<=n<=10⁵) . The second line contains one integer that corresponds to the bin length l<=10000 . We then have n lines containing one integer value that represents the length of the items.

Output
Your program has to write the minimal number of bins required to pack all items.

Sample Input

 

Sample Output

6

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
int n;
int a[100005];
int flag[100005];
int len;
int main()
...{
    int n;
    int cnt=0;
    scanf("%d",&n);
    int i,j,k;
    scanf("%d",&len);
    for(i=0;i<n;i++)
      scanf("%d",a+i);
    memset(flag,0,sizeof(flag));
    sort(a,a+n);
    for(i=0,j=n-1;i<=j;)
      if(a[i]+a[j]<=len) 
      ...{
            cnt++;i++;j--;
      }
       else 
      ...{
        cnt++;j--;     
       }
     
    
   cout<<cnt<<endl;
    return 0;
}

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• each bin contains at most 2 items,
  
• each item is packed in one of the q bins,
  
• the sum of the lengths of the items packed in a bin does not exceed l .

You are requested, given the integer values n , l , l1 , ..., ln , to compute the optimal number of bins q .