Question

此代码用于创建邻接列表（我认为），我想在向量中显示内容

#include<iostream>
#include<vector>
int main() {
    int N, M;
    fscanf( stdin, "%d%d", &N, &M );
    vector< int > graph[ N + 1 ];
    int i, u, v;
    for ( i = 0; i < M; ++i ) {
        fscanf( stdin, "%d%d", &u, &v );
        graph[ u ].push_back( v );
    }
    /*vector<int>iterator::it;
    for(it=graph.begin();it!=graph.end();it++)
    cout<<*it<<endl;*/
}

我尝试使用代码中注释的行显示输出但它给出了编译错误说：

struct std::iterator used without template parameters

您的帮助将不胜感激....

Answer 1

您可以在C ++向量中使用索引而不是迭代器。

for(int i=0;i<M;i++)
    cout<<graph[i]<<endl;

为了使用迭代器，您必须更正代码，例如：

#include<iostream>
#include<vector>
#include <stdio.h>
using namespace std;

int main() {
    int N, M;
    fscanf( stdin, "%d%d", &N, &M );
    vector<int> graph;
    int i, u, v;
    for ( i = 0; i < M; ++i ) {
        fscanf( stdin, "%d%d", &u, &v );
        graph.push_back(u);
        graph.push_back(v);
    }
    vector<int>::iterator it;
    for(it=graph.begin();it!=graph.end();it++)
    cout<<*it<<endl;
}

你的问题是在你的实例化中创建向量数组。

Answer 2

#include<iostream>
#include<vector>
int main() {
    int N, M;
    fscanf( stdin, "%d%d", &N, &M );
    std::vector< int > graph[ N + 1 ]; //try to use std::vector<std::vector<int>> - c kind array should have fixed (compilation time) size
    int i, u, v;
    for ( i = 0; i < M; ++i ) {
        fscanf( stdin, "%d%d", &u, &v );
        graph[ u ].push_back( v );
    }
    for ( int i = 0; i <= N; ++i){
        std::cout << i << ": ";
        for ( std::vector<int>::const_iterator it = graph[i].begin(); it != graph[i].end(); ++it){
            std::cout << *it << " ";
        }
    }
}
//try to use some compilation flag:
//-Wall -Wextra -Wpedantic -Wconversion -Wsign-conversion -Wfloat-equa

如何使用迭代器显示以下代码的输出？

2 个答案: