HDU 1051 Wooden Sticks

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

Wooden Sticks

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/32768 K (Java/Others)

Total Submission(s): 18724    Accepted Submission(s): 7680

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
  

 

Source

Asia 2001, Taejon (South Korea)

 

Recommend

思路：仔细读题，可以想到先按长度从小到大排个序，长度相同，再按重量从小到大排个序。那么对于一个没有被访问过的，计数加一，并标记为访问过，接着可以向后将满足条件(即不需要安装时间)的标记为访问过了。最终答案即为计数。详见代码。

附上AC代码：

#include <bits/stdc++.h>
#define pii pair<int, int>
#define f first
#define s second
using namespace std;
const int maxn = 5005;
pii num[maxn];
bool vis[maxn];
int n;

int main(){
	int T;
	scanf("%d", &T);
	while (T--){
		scanf("%d", &n);
		for (int i=0; i<n; ++i)
			scanf("%d%d", &num[i].f, &num[i].s);
		sort(num, num+n);
		memset(vis, false, sizeof(bool)*n);
		int ans = 0;
		for (int i=0; i<n; ++i)
			if (!vis[i]){
				++ans;
				vis[i] = true;
				int t = num[i].s;
				for (int j=i+1; j<n; ++j)
					if (!vis[j] && t<=num[j].s){
						vis[j] = true;
						t = num[j].s;
					}
			}
		printf("%d\n", ans);
	}
	return 0;
}