Wooden Sticks_贪心

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 18645    Accepted Submission(s): 7632

Problem Description

There is a pile of n wooden sticks. The length and weight of each stick are known in advance. The sticks are to be processed by a woodworking machine in one by one fashion. It needs some time, called setup time, for the machine to prepare processing a stick. The setup times are associated with cleaning operations and changing tools and shapes in the machine. The setup times of the woodworking machine are given as follows: 

(a) The setup time for the first wooden stick is 1 minute. 
(b) Right after processing a stick of length l and weight w , the machine will need no setup time for a stick of length l' and weight w' if l<=l' and w<=w'. Otherwise, it will need 1 minute for setup. 

You are to find the minimum setup time to process a given pile of n wooden sticks. For example, if you have five sticks whose pairs of length and weight are (4,9), (5,2), (2,1), (3,5), and (1,4), then the minimum setup time should be 2 minutes since there is a sequence of pairs (1,4), (3,5), (4,9), (2,1), (5,2).

 

Input

The input consists of T test cases. The number of test cases (T) is given in the first line of the input file. Each test case consists of two lines: The first line has an integer n , 1<=n<=5000, that represents the number of wooden sticks in the test case, and the second line contains n 2 positive integers l1, w1, l2, w2, ..., ln, wn, each of magnitude at most 10000 , where li and wi are the length and weight of the i th wooden stick, respectively. The 2n integers are delimited by one or more spaces.

 

Output

The output should contain the minimum setup time in minutes, one per line.

 

Sample Input

3 5 4 9 5 2 2 1 3 5 1 4 3 2 2 1 1 2 2 3 1 3 2 2 3 1

 

Sample Output

2 1 3

对木棍的长度和重量进行排序，以长度为首要考虑。排序完后的不一定都是下一根木棍重量和长度都大于前一根的。于是，我们对排序后的数组进行多次扫描，将可以在一次建立时间内完成的进行标记，知道木棍全部标记（设置一个外部变量来计数已扫描的元素的数量）。

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
struct stick
{
    int l,w;
}s[5000];
bool cmp(stick a,stick b)
{
    if(a.l<b.l) return true;
    else if(a.l>b.l) return false;
    else return a.w<b.w;
}
int main()
{
    int t,n,minn,ti;
    int vis[5000];
    cin>>t;
    while(t--)
    {
        cin>>n;
        for(int i=0;i<n;i++)
            cin>>s[i].l>>s[i].w;
        sort(s,s+n,cmp);
        memset(vis,0,sizeof(vis));
        int k=0;
        minn=0;
        int id;
        while(k!=n)
        {
            for(int i=0;i<n;i++)
            {
                if(!vis[i])
                {
                    id=i;
                    minn++;
                    break;
                }
            }
            for(int i=0;i<n;i++)
            {
                if(!vis[i]&&s[i].l>=s[id].l&&s[i].w>=s[id].w)
                {
                    vis[i]=1;
                    k++;
                    id=i;
                }
            }
        }
        cout<<minn<<endl;
    }
    return 0;
}