UVa 990 – Diving for Gold

Problem Link : https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=24&page=show_problem&problem=931

Solution Idea:

This is a classical knapsack problem. But in this problem we have to print the maximum profit as well as the detailed solution that is the maximum solution is obtained from which objects. Here the cost/weight is given by two equations like this-

• The descent time is tdi = w ∗ d[i] , where w is an integer constant.

• The ascent time is tai = 2w ∗ d[i] , where w is an integer constant.

So we can say that total cost/time need to get this treasure =  descent time+ascent time . which is w*d[i] + 2*w*d[i]=3*w*d[i].

Now we have to run a knapsack and we have to mark the objects which give me maximum profit. Now we have an array called path[][] which is initially set as -1 and it will mark the optimal objects. In knapsack function we have to variable p and q . where –

p= profit for taking current object

q=profit without current object

So if p>q then we will mark path[idx][air] = 1 else path[idx][air] = 2.

Now we have another function named path_print(idx, air) for getting the correct route of solution. In this function-

  • If path[idx][air] = 1 Then we will take the current objects and jump to  (idx+1, air+ 3*w*d[idx]) state.
  • If path[idx][air] = 2 then we will skip the current objects and jump to  (idx+1,air) state.
  • If path[idx][air] = -1 then we will stop because we already take the optimal objects.

/*
         +-+ +-+ +-+
         |R| |.| |S|
         +-+ +-+ +-+
 */

#include <bits/stdc++.h>

#define pii             pair <int,int>
#define sc              scanf
#define pf              printf
#define Pi              2*acos(0.0)
#define ms(a,b)         memset(a, b, sizeof(a))
#define pb(a)           push_back(a)
#define MP              make_pair
#define db              double
#define ll              long long
#define EPS             10E-10
#define ff              first
#define ss              second
#define sqr(x)          (x)*(x)
#define D(x)            cout<<#x " = "<<(x)<<endl
#define VI              vector <int>
#define DBG             pf("Hi\n")
#define MOD             100007
#define MAX             10000
#define CIN             ios_base::sync_with_stdio(0); cin.tie(0)
#define SZ(a)           (int)a.size()
#define sf(a)           scanf("%d",&a)
#define sfl(a)          scanf("%lld",&a)
#define sff(a,b)        scanf("%d %d",&a,&b)
#define sffl(a,b)       scanf("%lld %lld",&a,&b)
#define sfff(a,b,c)     scanf("%d %d %d",&a,&b,&c)
#define sfffl(a,b,c)    scanf("%lld %lld %lld",&a,&b,&c)
#define loop(i,n)       for(int i=0;i<n;i++)
#define REP(i,a,b)      for(int i=a;i<b;i++)
#define TEST_CASE(t)    for(int z=1;z<=t;z++)
#define PRINT_CASE      printf("Case %d: ",z)
#define all(a)          a.begin(),a.end()
#define intlim          2147483648
#define inf             1000000
#define ull             unsigned long long

using namespace std;


/*----------------------Graph Moves----------------*/
//const int fx[]={+1,-1,+0,+0};
//const int fy[]={+0,+0,+1,-1};
//const int fx[]={+0,+0,+1,-1,-1,+1,-1,+1};   // Kings Move
//const int fy[]={-1,+1,+0,+0,+1,+1,-1,-1};  // Kings Move
//const int fx[]={-2, -2, -1, -1,  1,  1,  2,  2};  // Knights Move
//const int fy[]={-1,  1, -2,  2, -2,  2, -1,  1}; // Knights Move
/*------------------------------------------------*/

/*-----------------------Bitmask------------------*/
//int Set(int N,int pos){return N=N | (1<<pos);}
//int reset(int N,int pos){return N= N & ~(1<<pos);}
//bool check(int N,int pos){return (bool)(N & (1<<pos));}
/*------------------------------------------------*/

int t,w,n;
int d[40],v[40];

int dp[40][1100];
int path[40][1100];

int func(int idx, int air)
{
    if(idx>=n) return 0;

    int &ret=dp[idx][air];
    if(ret!=-1) return ret;

    int p=0,q=0;

    if((air+(3*w*d[idx]))<=t)
        p=v[idx]+func(idx+1,air+(3*w*d[idx]));
    q=func(idx+1,air);

    if(p>q) path[idx][air]=1;
    else path[idx][air]=2;

    return ret=max(p,q);
}

vector<int>ans;

int path_print(int idx, int air)
{
    if(path[idx][air]==-1) return 0;

    if(path[idx][air]==1)
    {
        ans.pb(idx);
        return 1+path_print(idx+1,air+(3*w*d[idx]));
    }
    else
        return path_print(idx+1,air);
}

int main()
{
//    freopen("in.txt","r",stdin);
//    freopen("out.txt","w",stdout);

    bool test=0;

    while(sff(t,w)==2)
    {
        if(test==1) pf("\n");
        test=1;
        sf(n);
        loop(i,n) sff(d[i],v[i]);
        ms(dp,-1);
        ms(path,-1);
        int profit=func(0,0);

        pf("%d\n",profit);
        pf("%d\n",path_print(0,0));
        loop(i,SZ(ans))
        pf("%d %d\n",d[ans[i]],v[ans[i]]);
        ans.clear();
    }

    return 0;
}


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