PKUOJ1065 Wooden Sticks

Wooden Sticks

Time Limit:1000MS		Memory Limit:10000K
Total Submissions:11794		Accepted:4808

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 ( 9 , 4 ) , ( 2 , 5 ) , ( 1 , 2 ) , ( 5 , 3 ) , and ( 4 , 1 ) , then the minimum setup time should be 2 minutes since there is a sequence of pairs ( 4 , 1 ) , ( 5 , 3 ) , ( 9 , 4 ) , ( 1 , 2 ) , ( 2 , 5 ) .

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 2n 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

【题意】

有n根木棍，每根木棍有不同的长度和重量。用一台机器来处理这些木棍，当第i+1根木棍的长度>=第i根木棍的长度 && 第i+1根木棍的重量>=第i根木棍的重量时，机器处理木棍的单位时间setup time加1，求出处理完n根木棍所需要的最少时间

【题解】

按木棍的长度从小到大排序，当木棍长度相等时，按重量小到大排序。然后依次选择比当前长度大的木棍（已经对木棍进行排序，每次选择都是对后面影响最小的），对选过的木棍进行标记。一轮之后，setup time+1，再对剩下的木棍进行选择，即可得到最优解。

#include <iostream> using namespace std; struct wood { int l; int w; }st[5005]; int work(int m) { int temp; int sum=0; for (int i =0;i<m;++i) { if (st[i].w!=-1) { temp = st[i].w; sum++; for (int j=i+1;j<m;++j) { if (st[j].w>=temp) { temp=st[j].w; st[j].w=-1; } } } } return sum; } //比较函数 int cmp(const void *a ,const void *b) { if((*(wood *)a).l==(*(wood*)b).l) return (*(wood *)a).w -(*(wood *)b).w; return (*(wood *)a).l - (*(wood *)b).l; } int main() { int n,m; cin>>n; while (n--) { cin>>m; for (int i=0;i<m;++i) { cin>>st[i].l>>st[i].w; } qsort(st,m,sizeof(st[0]),cmp); cout<<work(m)<<endl; } return 0; }