HDU 1051 Wooden Sticks

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贪心

Wooden Sticks

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 21402    Accepted Submission(s): 8636

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

213

题目的意思是有n根木头，每根木头都有自己的长度和重量，机器只能处理长度和重量都比第一根木头大的木头，不然就要重新设定，重新设定就要增加时间。问处理完所有的木头总共需要多长时间。

贪心，首先按照长度给木材排序，然后记录第一根木材，遍历，把能处理的木材都处理掉，，然后进行第二轮处理，再遍历，以此类推，直到木材都处理完毕。

代码实现：

#include<iostream>#include<algorithm>#include<cstring>using namespace std;struct node{int l,w;}p[10005];int cmp(node a,node b){if(a.l==b.l)return a.w<b.w;return a.l<b.l;}int main(){int t,n,i,j,k,v[10005],flag;cin>>t;while(t--){long long sum=0;cin>>n;for(i=0;i<n;i++)cin>>p[i].l>>p[i].w;memset(v,0,sizeof(v));sort(p,p+n,cmp);v[0]=1;k=0;while(k<n){++sum;for(i=k+1,j=k,flag=1;i<n;++i){if(v[i])continue;if((p[j].w<=p[i].w)&&(p[j].l<=p[i].l)){v[i]=1;j=i;}else{if(flag){flag=0;k=i;}}}if(flag)break;}cout<<sum<<endl;}return 0;}