HDU-1051Wooden Sticks （贪心）

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 ( 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

213
贪心：把木头把l从大到小排序，l相同的w从大到小排序。然后记录第一个没有用到的木头。然后顺序找，再回过头来从没有用到的木头再顺序找，直到全部找完。
#include <iostream>#include <algorithm>#include <string.h>#include <stdio.h>#include <set>#include <cmath>#include <queue>using namespace std;const int maxn = 5005;struct Node {    int l, w;}node[maxn];int visited[maxn];bool cmp(const Node& n1, const Node& n2) {    return n1.l < n2.l || (n1.l == n2.l && n1.w < n2.w);}int main() {        //freopen("in.txt", "r", stdin);    int t;    cin >> t;    while (t--) {        int n;        cin >> n;        for (int i = 0; i < n; ++i) {            cin >> node[i].l >> node[i].w;        }        sort(node, node + n, cmp);        int ans = 0;        int start = 0, flag = 0;//start记录第一个没有用到的木头        memset(visited, 0, sizeof(visited));        while (start < n) {            ans++;            flag = 1;            for (int i = start + 1, j = start; i < n; ++i) {                if (visited[i])                    continue;                if (node[i].l >= node[i].l && node[i].w >= node[j].w) {                    j = i;                    visited[i] = 1;                } else {                    if (flag) {                        start = i;                        visited[i] = 1;                        flag = 0;                    }                }            }            //如果不存在没有用到的木头，就break            if (flag)                break;        }        cout << ans << endl;    }}