1408111855-hd-Wooden Sticks.cpp

最新推荐文章于 2019-08-01 12:48:26 发布

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本文探讨了一堆木头进行加工时如何找到最短的准备时间，通过将木头按长度和重量排序并使用贪心算法和动态规划解决这个问题。

Wooden Sticks

Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others)
Total Submission(s): 11664 Accepted Submission(s): 4828

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

题目大意

有一堆木头要进行加工，他们的长度和宽度都不相同，在进行加工的时候，若下一根木头的长度和宽度都不小于此时的木头，则机器不用调整，反之则需要调整机器，每一次调整需要一分钟，要求最短时间。

错误原因

没理解清除题意，哎，，，，英语是硬伤啊！

解题思路

要求最短时间明显需要贪心算法，先对长度和宽度做升序排列，然后开始比较，但是需要记住一点，这是求一个最长递增序列，所以每次比较的都是前一跟木头的长度和宽度，所以这题需要再定义一个动态的变量nowl,noww来记录每次比较之后的长度和宽度，所以这题也用到了动态规划。

代码

#include<stdio.h>
#include<algorithm>
using namespace std;
struct wooden
{
    int l,w;
}wd[5100];
bool cmp(wooden a,wooden b)
{
    if(a.l!=b.l)
        return a.l<b.l;
    else
        return a.w<b.w;
}
int main()
{
    int t;
    int n;
    int i,j,nowl,noww,sum;
    scanf("%d",&t);
    while(t--)
    {
        scanf("%d",&n);
        for(i=0;i<n;i++)
            scanf("%d%d",&wd[i].l,&wd[i].w);
        sort(wd,wd+n,cmp);
        sum=0;
        for(i=0;i<n;i++)
        {
            if(wd[i].l!=-1&&wd[i].w!=-1)
            {
                nowl=wd[i].l;
                noww=wd[i].w;
                sum++;
                for(j=i+1;j<n;j++)
                {
                    if(nowl<=wd[j].l&&noww<=wd[j].w)
                    {
                        nowl=wd[j].l;
                        noww=wd[j].w;
                        wd[j].l=-1;
                        wd[j].w=-1;
                    }
                }
            }
        }
        printf("%d\n",sum);
    }
    return 0;
}