int example(Graph G, int i, int j, int len) { if (len < 0) return 0; if (i == j && len == 0) return 1; sum = 0; visited[i] = 1; for (Edge e = G.FirstEdge(i); G.IsEdge(e); e = G.NextEdge(e)) { int index = G.ToVertex(e); if (!visited[index]) sum += example (G, index, j, len - 1); } visited[i] = 0; // 语句 return sum; }这段代码啥意思
时间: 2024-03-31 08:38:23 浏览: 18
这段代码实现了一个在给定有向图中,从顶点 i 出发,经过 len 条边到达顶点 j 的路径数量的计算。其中,变量 visited 数组记录了每个顶点是否已经被访问过,变量 sum 记录了符合条件的路径数量。具体实现是通过递归函数 example 来完成的。如果 len 小于 0,说明已经经过了指定的边数,但仍未到达 j,这种情况下返回 0;如果 i 等于 j 且 len 等于 0,说明已经到达了 j 且经过了指定的边数,返回 1;否则,遍历从 i 出发能够到达的所有顶点,并递归调用 example 函数,累计符合条件的路径数量,最终返回 sum。在递归调用之前,需要将 visited[i] 置为 1,表示 i 已经被访问过,在递归调用之后,需要将 visited[i] 置为 0,表示 i 已经被撤销访问。
相关问题
#include <cstdio> #include <cstring> #include <algorithm> using namespace std; const int MAXN = 107; const int INF = 0x3f3f3f3f; typedef long long ll; int graph[MAXN][MAXN]; int main() { int n, e; while (~scanf("%d %d", &n, &e)) { memset(graph, INF, sizeof(graph)); for (int i = 1; i <= e; i++) { int from, to, v; scanf("%d %d %d", &from, &to, &v); ++from, ++to; if (from == to) { graph[from][to] = 0; } else { graph[from][to] = v; graph[to][from] = v; } } for (int k = 1; k <= n; k++) { for (int i = 1; i <= n; i++) { for (int j = 1; j <= n; j++) { if (graph[i][j] > graph[i][k] + graph[k][j]) { graph[i][j] = graph[i][k] + graph[k][j]; } } } } ll dis[MAXN] = {0}; for (int i = 1; i <= n; i++) { for (int j = 1; j <= n; j++) { if (i != j) { dis[i] += (ll)graph[i][j]; } } } ll min_dis = INF; int min_pos = 1; for (int i = 1; i <= n; i++) { if (dis[i] < min_dis) { min_dis = dis[i]; min_pos = i; } } --min_pos; printf("%d\n", min_pos); } return 0; }帮我把这段代码转换为c++
在这里提供一份已经是 C++ 代码的版本,可以直接使用:
```cpp
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
const int MAXN = 107;
const int INF = 0x3f3f3f3f;
typedef long long ll;
int graph[MAXN][MAXN];
int main() {
int n, e;
while (cin >> n >> e) {
memset(graph, INF, sizeof(graph));
for (int i = 1; i <= e; i++) {
int from, to, v;
cin >> from >> to >> v;
++from, ++to;
if (from == to) {
graph[from][to] = 0;
} else {
graph[from][to] = v;
graph[to][from] = v;
}
}
for (int k = 1; k <= n; k++) {
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= n; j++) {
if (graph[i][j] > graph[i][k] + graph[k][j]) {
graph[i][j] = graph[i][k] + graph[k][j];
}
}
}
}
ll dis[MAXN] = {0};
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= n; j++) {
if (i != j) {
dis[i] += (ll)graph[i][j];
}
}
}
ll min_dis = INF;
int min_pos = 1;
for (int i = 1; i <= n; i++) {
if (dis[i] < min_dis) {
min_dis = dis[i];
min_pos = i;
}
}
--min_pos;
cout << min_pos << endl;
}
return 0;
}
```
void DFSTraverse(Graph graph) { for (int i = 1; i <= graph->vexnum; i++) visited[i] = false; for (int i = 1; i <= graph->vexnum; i++) { if (!visited[i]) DFS(graph, i); } } void DFS(Graph graph, int v) { visited[v] = true; cout << graph->list[v].data << " "; Node* header = graph->list[v].head; while (header) { if (!visited[header->vex]) { DFS(graph, header->vex); } header = header->next; } } void BFSTraverse(Graph graph) { queue<int> MyQueue; for (int i = 1; i <= graph->vexnum; i++) visited[i] = false; for (int i = 1; i <= graph->vexnum; i++) { if (!visited[i]) { visited[i] = true; cout << graph->list[i].data << " "; MyQueue.push(i); while (!MyQueue.empty()) { int front = MyQueue.front(); MyQueue.pop(); Node* header = graph->list[front].head; while (header) { if (!visited[header->vex]) { visited[header->vex] = true; cout << graph->list[header->vex].data << " "; MyQueue.push(header->vex); } header = header->next; } } } } } void printGraph(Graph graph) { int** arr = new int* [graph->vexnum + 1]; for (int i = 1; i <= graph->vexnum; i++) { arr[i] = new int[graph->vexnum + 1]; } for (int i = 1; i <= graph->vexnum; i++) { for (int j = 1; j <= graph->vexnum; j++) { arr[i][j] = 0; } } for (int i = 1; i <= graph->vexnum; i++) { Node* header = graph->list[i].head; while (header) { arr[i][header->vex] = header->weight; header = header->next; } } for (int i = 1; i <= graph->vexnum; i++) { for (int j = 1; j <= graph->vexnum; j++) { cout << arr[i][j] << " "; } cout << endl; } }代码讲解
DFSTraverse函数和DFS函数实现了图的深度优先遍历。首先将visited数组初始化为false,然后对每个顶点进行深度优先遍历。在DFS函数中,首先将当前顶点标记为已访问,并输出其数据。然后遍历当前顶点的邻接表,对于每个未被访问过的邻接点,递归调用DFS函数进行遍历。
BFSTraverse函数实现了图的广度优先遍历。同样先将visited数组初始化为false,然后对每个未被访问过的顶点进行广度优先遍历。在遍历每个顶点时,将其标记为已访问,输出其数据,并将其加入队列中。然后对队列中的元素依次出队,并遍历其邻接表,对于每个未被访问过的邻接点,将其标记为已访问,输出其数据,并将其加入队列中。
printGraph函数用于输出图的邻接矩阵。首先动态创建一个二维数组arr来存储邻接矩阵。然后将其初始化为0。接着遍历每个顶点的邻接表,将对应的邻接矩阵元素赋值为边的权重。最后输出邻接矩阵。