Blue Bridge: souvenirs packet (Center Weighted greedy algorithm for ordering +)

Souvenirs packet (greedy algorithm Center Weighted + sort)

Problem Description

　　New Year's Day approaching, the school will learn ⽣ Lele souvenir New Year's party in charge of issuing ⼯ for. So the students to the party obtained

Souvenirs value is relatively balanced, he wanted to buy souvenirs into ⾏ grouped according to price, but each group can include up to two souvenirs, and

And the price of each set of souvenirs and can not exceed ⼀ a given integer. In order to ensure that within the shortest possible time finished all the souvenirs, music

Le hopes minimum number of packet destination time.

　　Your task is to write ⼀ a program to find the minimum number of packets all packets ⽅ case ⼀ species, the minimum number of packets output destination time.

START input format

　　START input comprising n + 2 ⾏:

　　The first 1 ⾏ include

⼀ integers W , each of souvenirs and a price limit.

　　Of 2 ⾏ is ⼀ integers n- , it represents the total number of items available to souvenirs.

　　Of 3 ~ n + 2 ⾏ each ⾏ Contains either positive integer pi (5 <= pi <= w), corresponding Prices souvenirs.

Output Format

　　Outputs only ⼀ ⾏, Contains either integer, i.e., the minimum number of packets destination time.

Sample lose START

100

9

90

20

20

30

50

60

70

80

90

Sample Output

6

Scale data and conventions

　　50% of the full data EMPTY: . 1 <= n-<= 15

　　100% of the full data EMPTY: . 1 <= n-<= 30000, 80 <= W <= 200 is

 

 

Analysis: + greed Center Weighted Sort. ⼩ to start sorting zoomed, i, j pointers are from left to right, right to left traversal.

If a [i] + a [j] <= w, then these two items are placed with START ⼀ group, and moves the pointer at the same time;

Otherwise, only the j points to a separate article release START ⼀ groups, move the pointer j ij ... until all items are traversed ~

Note: Each group only two items, according to the meaning of problems

 

#include <iostream>
#include <algorithm>
#include <cstdio>
using namespace std;
int main() {
 int w, n;
 scanf("%d %d", &w, &n);
 int *a = new int[n];
 for( int i = 0; i < n; i++)
      scanf("%d", &a[i]);
 sort(a, a+n);
 int i = 0, j = n-1, cnt = 0;
 while( i <= j) {
    if( a[i] + a[j] <= w) {
        i++;
    }
    cnt++;
    j--;
 }
 cout << cnt;
 return 0; 
}