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).
(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
1 #include<stdio.h> 2 #include<stdlib.h> 3 #include<string.h> 4 #define N 5000; 5 6 struct node 7 { 8 int l; 9 int w; 10 int flag; 11 }sticks[5000]; 12 int cmp(const void *p,const void *q) 13 { 14 struct node *a = (struct node *)p; 15 struct node *b = (struct node *)q; 16 if(a->l > b->l) return 1; 17 else if(a->l < b->l) return -1; 18 else return a->w > b->w ? 1 : -1; 19 } 20 int main() 21 { 22 int t,n,cnt,cl,cw; 23 int i,j; 24 scanf("%d",&t); 25 while(t--) 26 { 27 memset(sticks,0,sizeof(sticks)); 28 scanf("%d",&n); 29 for( i = 0; i < n; i++) 30 scanf("%d %d",&sticks[i].l,&sticks[i].w); 31 qsort(sticks,n,sizeof(sticks[0]),cmp); 32 sticks[0].flag = 1; 33 cl = sticks[0].l; 34 cw = sticks[0].w; 35 cnt = 1; 36 for( j = 1; j < n; j++) 37 { 38 for( i = j; i < n; i++) 39 { 40 if(!sticks[i].flag&&sticks[i].l>=cl&&sticks[i].w>=cw) 41 { 42 cl = sticks[i].l; 43 cw = sticks[i].w; 44 sticks[i].flag = 1; 45 } 46 } 47 i = 1; 48 while(sticks[i].flag) 49 i++; 50 j = i; 51 if(j == n) break; 52 cl = sticks[j].l; 53 cw = sticks[j].w; 54 sticks[j].flag = 1; 55 cnt++; 56 } 57 printf("%d\n",cnt); 58 59 } 60 return 0; 61 }
题意：
我们要处理一些木棍，第一根的时间是1分钟，另外的，在长度为l，重为w的木棍后面的那根的长度为l’, 重量w’，只要l <=l’ 并且w <= w’，就不需要时间，否则需要1分钟，求如何安排处理木棍的顺序，才能使花的时间最少。
思路：
贪心算法。先把这些木棍按长度和重量都从小到大的顺序排列。cl和cw是第一根的长度和重量，依次比较后面的是不是比当前的cl，cw大，是的话把标志flag设为1，并跟新cl,cw。比较完后，再从前往后扫描，找到第一个标志位为0的，作为是第二批的最小的一根，计数器加一。把它的长度和重量作为当前的cl，cw，再循环往后比较。直到所有的都处理了。