hdu1051：Wooden Sticks（贪心）

http://acm.hdu.edu.cn/showproblem.php?pid=1051

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

题意分析：

有n个木棍，已知它们的长度和重量，现在要把它们一一加工，每个木棍有一个设置时间。

设置时间与清洁操作和更改机器中的工具和形状有关，设置时间的规定：

a.第一个加工的木棍的设置时间为1；

b.在加工了长度为 l 重量为 w 的木棍之后，如果下一个加工的木棍的长度和重量都不小于前一个，就不需要设置时间，

否则需要1分钟的设置时间。

求把所有木棍加工完需要的最小的设置时间。

解题思路：

按照长度排个序，如果长度相同，按照重量排序。

如果后面一个木棍的长度和重量有一个小于前面的，另外考虑，

首先挑出长度最短的一个，从后面找出最近的一个符合条件的，找到最后还有剩余就重复前面的过程，直到所有的木棍都被加工完成。

#include <stdio.h>
#include <string.h>
#include <algorithm>
using namespace std;
#define N 5050
struct data{
	int w;
	int l;
}a[N], t;
int book[N];
int cmp(data a, data b)
{
	if(a.l!=b.l)
		return a.l<b.l;
	return a.w<b.w;
}
int main()
{
	int T, n, i, j, ans;
	scanf("%d" ,&T);
	while(T--)
	{
		scanf("%d", &n);
		for(i=0; i<n; i++)
			scanf("%d%d", &a[i].l, &a[i].w);
		sort(a, a+n, cmp);
		memset(book, 0, sizeof(book));
		j=0;
		ans = 0;
		while(j<n)
		{
			for(i=0; i<n; i++)
				if(book[i]==0)
				{
					t=a[i];
					book[i] = 1;
					j++;
					ans++;
					break;
				}
			i++;
			for(; i<n; i++)
			{
				if(a[i].l>=t.l && a[i].w>=t.w && book[i]==0)
				{
					j++;
					book[i] = 1;
					t=a[i];
				}
			}					
		}
		printf("%d
", ans);
	}
	return 0;
}