uva 10123

这题的题意是 在双脚天平上有N块东西，依次从上面取走一些，最后使得这个天平保持平衡！

解题：

　　逆着来依次放入，如果可行那就可以，记得得有木板自身的重量。

/*************************************************************************
    > File Name: 10123.cpp
    > Author: opas
    > Mail: 1017370773@qq.com 
    > Created Time: 2016年10月22日 星期六 22时58分53秒
 ************************************************************************/
#include<cstdio>
#include<string.h>
#include<algorithm>
#include<iostream>
using namespace std;
const int maxm = 20;
const int maxn = 1<<maxm;
struct Node {
    int id,weight,dist;
    Node (int l_id = 0, int l_weight = 0, int l_dist = 0)    {
        id = l_id;
        weight = l_weight;
        dist = l_dist;
    }
    bool operator < (const Node A)const {
        if (weight != A.weight ) return weight < A.weight;
        return id < A.id;
    }
}package[maxm];
int dp[maxn];
int weight_val[maxn][4];
int ans[maxm];
void InitVal(int n)    {
    int max_val = 1<<n;
    for(int i = 0; i < max_val; ++ i)    {
        dp[i] = 0;
    }
}
int length ,weight, num_package;
void AddPackage(int per_status ,int now_status, int id)    {
    for ( int i = 0; i < 4; ++ i)
        weight_val[now_status][i] = weight_val[per_status][i];
    if(package[id].dist <= -3)    {
        weight_val[now_status][0] = weight_val[per_status][0] + - ( package[id].dist + 3) * package[id].weight; 
        weight_val[now_status][3] = weight_val[per_status][3] + - ( package[id].dist - 3) * package[id].weight;
    }else if(package[id].dist < 3){
        weight_val[now_status][1] = weight_val[per_status][1] + (package[id].dist + 3) * package[id].weight;
        weight_val[now_status][3] = weight_val[per_status][3] + - (package[id].dist - 3) * package[id].weight;
    }else{
        weight_val[now_status][1] = weight_val[per_status][1] + (package[id].dist + 3)*package[id].weight;
        weight_val[now_status][2] = weight_val[per_status][2] + (package[id].dist - 3)*package[id].weight;
    }
}
int CheckPackage(int now_status)    {
    int l_val1 = weight_val[now_status][0];
    int l_val2 = weight_val[now_status][1] +3 * weight;
    if(l_val1 > l_val2){
      return dp[now_status] = 2; 
    }
    l_val1 = weight_val[now_status][2];
    l_val2 = weight_val[now_status][3] + 3 * weight;
    if(l_val1 > l_val2) {
        return dp[now_status] = 2;
    }
        return dp[now_status] = 1;
}
int dfs(int now_loc, int now_status)    {
    if(now_loc == num_package)    {
        return 1; 
    }
    dp[now_status] = 2;
    for(int i = 0; i< num_package ; ++ i)    {
        if(now_status & (1<<i)) 
            continue;
        int next_status = now_status | (1<<i);
        if(dp[next_status] == 2) return dp[next_status];
        AddPackage(now_status, next_status, i);
        if(CheckPackage(next_status) == 2) 
            continue;
        ans[now_loc] = i;
        if (dfs(now_loc+1, next_status) == 1)    {
            return dp[now_status]=1;
        } 
    }
    return 2;
}
int main(){     
    for(int cc = 1; ; ++ cc) {    
        cin>>length>>weight>>num_package;
        if(length + weight + num_package == 0)
                break;
        InitVal(num_package);
        for(int i = 0; i < num_package; ++ i)    {
            int l_weight , l_dist;
            scanf("%d%d",&l_dist, &l_weight);    
            l_dist = l_dist * 2;
            package[i] = Node(i, l_weight, l_dist);
        }
        printf("Case %d:
",cc);
        if( dfs(0 , 0) == 1) {
            for(int i = num_package - 1; i >= 0; -- i)    {
                printf("%d %d
", package[ans[i]].dist/2, package[ans[i]].weight);
            } 
        }else{
            printf("Impossible
");
        }
    }
    return 0;
}