C++~回溯+贪心法解决01背包问题

如果是写作业找到了我这里，希望不要直接copy~仅供参考~可能有错误的，自己写帮助很大^0^

#include
#include<string.h>
#include
using namespace std;
struct item{
    double weight,value;
    int index;
};
struct item items[101];
int x[101];
int res[101];
int n;
double c;
double max_value;
bool isOk(int t){
    int i,j;
    double max_c=c,max_v=0;
    for(i=0;i<=t;i++){
        if(x[i]==1){
            max_v+= items[i].value;
            max_c-= items[i].weight;
        }
        if(max_c < 0){
            return false;
        }
    }

    for(;i<=n-1;i++){
        if(max_c >= items[i].weight){
            max_v+= items[i].value;
            max_c-= items[i].weight;
        } else {
            max_v=max_v+( max_c*(items[i].value/items[i].weight) );
            max_c=0;
            break;
        }
    }
    if(max_v < max_value)
        return false;
    return true;
}
void backtrack(int t){
    int j;
    if(t>=n){
        double cur=0;
        for(j=0;j){
            if(x[j]==1)
                cur+=items[j].value;
        }
        if(cur>max_value){
            max_value = cur;
            for(j=0;j){
                res[j]=x[j];
            }
        }
        return;
    }
    for(int i=1;i>=0;i--){
        x[t]=i;
        if(isOk(t)){
            backtrack(t+1);
        }
    }
}
void swap(int i,int j){
    struct item temp;
    temp = items[i];
    items[i] = items[j];
    items[j] = temp;
}
void sort(int left,int right){
    if(left > right)
        return;
    int i,j;
    struct item temp;
    i=left;
    j=right;
    temp = items[left];
    while(i!=j){
        while(items[j].value/items[j].weight <= temp.value/temp.weight && i<j){
            j--;
        }
        while(items[i].value/items[i].weight >= temp.value/temp.weight && i<j){
            i++;
        }
        if(i<j){
            swap(i,j);
        }
    }
    items[left] = items[i];
    items[i] = temp;
    sort(left,i-1);
    sort(i+1,right);
}
void displayRes(){
    for(int i=0;i<=n-1;i++){
        for(int j=0;j<=n-1;j++){
            if(items[j].index == i){
                cout<" ";
                break;
            }
        }
    }
    cout<<endl;
}
int main(){
    cin>>c>>n;
    max_value=0;
    for(int i=0;i){
        cin>>items[i].weight>>items[i].value;
        items[i].index=i;
        x[i]=0;
        res[i]=0;
    }
    sort(0,n-1);
    backtrack(0);
    displayRes();
    cout<endl;
}

 

转载于:https://www.cnblogs.com/rimochiko/p/8168638.html