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B&B_Knapsack.cpp
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B&B_Knapsack.cpp
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#include <iostream>
#include <string>
#include <sstream>
#include <fstream>
#include <vector>
#include <stdio.h>
#include <utility>
#include <algorithm>
using namespace std;
bool compare(pair<float, int> a, pair<float, int> b)
{
return a.first >= b.first;
}
struct input
{
input(int nn = 0, int KK = 0)
{
n = 0;
K = KK;
alloc(nn);
}
void alloc(int nn)
{
if(n > 0)
{
delete[] v;
delete[] w;
}
v = 0;
w = 0;
if(nn > 0)
{
v = new int[nn];
w = new int[nn];
order.reserve(nn);
}
n = nn;
}
~input()
{
if(v) delete v;
if(w) delete w;
}
void set_order()
{
for(int i = 0; i < n; ++i) order.push_back(make_pair(float(v[i]) / float(w[i]), i));
sort(order.begin(), order.end(), compare);
}
int n;
int K;
int *v;
int *w;
vector< pair<float, int> > order;
};
struct output
{
output(int nn = 0)
{
n = 0;
alloc(nn);
}
void alloc(int nn)
{
obj = 0;
opt = 0;
if(n > 0) delete[] x;
x = 0;
if(nn > 0)
{
x = new int[nn];
for(int i = 0; i < nn; ++i) x[i] = 0;
}
n = nn;
}
~output()
{
if(x) delete[] x;
}
int obj;
int opt;
int n;
int *x;
};
void solve(input &in, output &out, output &best_out, int j, int current_val, int current_weight, int &best)
{
int best_possible(0);
int aux_weight(current_weight);
int next_weight(0);
//cout<<"Estamos en: x_"<<(j < in.n ? in.order[j].second : -1)<<endl;
if(j == in.n)
{
if(current_val > best)
{
best = current_val;
best_out.obj = current_val;
best_out.opt = 1;
for(int i = 0; i < out.n; ++i) best_out.x[i] = out.x[i];
//cout<<"Esta hoja define un nuevo minimo: "<<best<<endl;
}
return;
}
else
{
best_possible = current_val;
for(int i = j; i < in.n; ++i)
{
if(aux_weight >= in.K) break;
next_weight = min(in.K - aux_weight, in.w[in.order[i].second]);
aux_weight += next_weight;
best_possible += next_weight * in.order[i].first;
}
if(best_possible < best) return;
out.x[in.order[j].second] = 0;
solve(in, out, best_out, j + 1, current_val, current_weight, best);
if(in.w[in.order[j].second] + current_weight <= in.K)
{
out.x[in.order[j].second] = 1;
solve(in, out, best_out, j + 1, current_val + in.v[in.order[j].second], current_weight + in.w[in.order[j].second], best);
out.x[in.order[j].second] = 0;
}
}
}
/*
output solve2(input &in)
{
int **table = new int*[2];
int *aux_row(0);
int *backtrace(0);
int max[2] = {0,0};
output out(in.n);
backtrace = new int[in.n];
table[0] = new int[in.K + 1];
table[1] = new int[in.K + 1];
for(int i = 0; i <= in.K; ++i) table[1][i] = 0;
// Over every element [0, ..., n -1].
for(int i = 0; i < in.n; ++i)
{
aux_row = table[0];
table[0] = table[1];
table[1] = aux_row;
max[0] = -9999999;
// Over every capacity [0, ..., K].
for(int k = 0; k <= in.K; ++k)
{
// If the weight does not fit in the capacity, then just copy the value of the previous object.
// Else the maximum between using this object and not using it.
if(k < in.w[i]) table[1][k] = table[0][k];
else table[1][k] = (table[0][k] > table[0][k - in.w[i]] + in.v[i] ? table[0][k] : table[0][k - in.w[i]] + in.v[i]);
if(table[1][k] > max[0])
{
max[0] = table[1][k];
max[1] = k;
}
}
for(int k = 0; k <= in.K; ++k) cout<<table[1][k]<<"\t";
cout<<endl;
// Adjust the backtrace.
backtrace[i] = max[1];
if(i > 0 && table[0][max[1]] < table[1][max[1]])
{
int d = backtrace[i - 1] + in.w[i] - backtrace[i];
for(int h = 0; h < i; ++h) backtrace[h] -= d;
}
}
out.obj = table[1][in.K];
for(int i = 0; i < in.n; ++i) {out.x[i] = backtrace[i]; cout<<backtrace[i]<<" ";}
delete table[0];
delete table[1];
delete table;
delete backtrace;
return out;
}
*/
int main(int argc, char **argv)
{
string file_name = argc > 1 ? argv[1] : "knapsack_instances/ks_400_0";
ifstream file;
int n(0), K(0);
input in;
output out, best_out;
int best(-1);
file.open(file_name.c_str(), ios::in);
file>>n;
file>>K;
in.K = 20000;
in.alloc(n);
for(int i = 0; i < n; ++i)
{
file>>in.v[i];
file>>in.w[i];
}
file.close();
in.set_order();
out.alloc(in.n);
best_out.alloc(in.n);
cout<<"n="<<in.n<<" K="<<in.K<<endl;
solve(in, out, best_out, 0, 0, 0, best);
cout<<best_out.obj<<endl;
//for(int i = 0; i < out.n; ++i) cout<<best_out.x[i]<<(i < out.n - 1 ? " " : "");
return 0;
}