给定一个图G由N 个节点组成,一个源S和一个类型为{u, v}的数组Edges[][2]表示节点u和v之间存在无向边,任务是遍历使用 DFS 按字典顺序绘制图形。
例子:
Input: N = 10, M = 10, S = ‘a’, Edges[][2] = { { ‘a’, ‘y’ }, { ‘a’, ‘z’ }, { ‘a’, ‘p’ }, { ‘p’, ‘c’ }, { ‘p’, ‘b’ }, { ‘y’, ‘m’ }, { ‘y’, ‘l’ }, { ‘z’, ‘h’ }, { ‘z’, ‘g’ }, { ‘z’, ‘i’ } }
Output: a p b c y l m z g h i
Explanation:
For the first level visit the node and print it:
Similarly visited the second level node p which is lexicographical smallest as:
Similarly visited the third level for node p in lexicographical order as:
Now the final traversal is shown in the below image and labelled as increasing order of number:
Input: N = 6, S = ‘a’, Edges[][2] = { { ‘a’, ‘e’ }, { ‘a’, ‘d’ }, { ‘e’, ‘b’ }, { ‘e’, ‘c’ }, { ‘d’, ‘f’ }, { ‘d’, ‘g’ } }
Output: a d f g e b c
处理方法:按照以下步骤解决问题:
- 初始化一个映射,比如G以根据节点的字典顺序存储一个节点的所有相邻节点。
- 初始化一个地图,比如vis检查一个节点是否已经被遍历。
- 遍历 Edges[][2] 数组,并将图的每个节点的所有相邻节点存储在G 中。
- 最后,使用 DFS 遍历图形并打印图形的访问节点。
下面是上述方法的实现:
C++
// C++ program for the above approach
#include
using namespace std;
// Function to traverse the graph in
// lexicographical order using DFS
void LexiDFS(map >& G,
char S, map& vis)
{
// Mark S as visited nodes
vis[S] = true;
// Print value of visited nodes
cout << S << " ";
// Traverse all adjacent nodes of S
for (auto i = G[S].begin();
i != G[S].end(); i++) {
// If i is not visited
if (!vis[*i]) {
// Traverse all the nodes
// which is connected to i
LexiDFS(G, *i, vis);
}
}
}
// Utility Function to traverse graph
// in lexicographical order of nodes
void CreateGraph(int N, int M, int S,
char Edges[][2])
{
// Store all the adjacent nodes
// of each node of a graph
map > G;
// Traverse Edges[][2] array
for (int i = 0; i < M; i++) {
// Add the edges
G[Edges[i][0]].insert(
Edges[i][1]);
}
// Check if a node is already
// visited or not
map vis;
// Function Call
LexiDFS(G, S, vis);
}
// Driver Code
int main()
{
int N = 10, M = 10, S = 'a';
char Edges[M][2]
= { { 'a', 'y' }, { 'a', 'z' },
{ 'a', 'p' }, { 'p', 'c' },
{ 'p', 'b' }, { 'y', 'm' },
{ 'y', 'l' }, { 'z', 'h' },
{ 'z', 'g' }, { 'z', 'i' } };
// Function Call
CreateGraph(N, M, S, Edges);
return 0;
}
Java
// Java program for above approach
import java.util.*;
class Graph{
// Function to traverse the graph in
// lexicographical order using DFS
static void LexiDFS(HashMap> G,
char S, HashMap vis)
{
// Mark S as visited nodes
vis.put(S, true);
// Print value of visited nodes
System.out.print(S + " ");
// Traverse all adjacent nodes of S
if (G.containsKey(S))
{
for(char i : G.get(S))
{
// If i is not visited
if (!vis.containsKey(i) || !vis.get(i))
{
// Traverse all the nodes
// which is connected to i
LexiDFS(G, i, vis);
}
}
}
}
// Utility Function to traverse graph
// in lexicographical order of nodes
static void CreateGraph(int N, int M, char S,
char[][] Edges)
{
// Store all the adjacent nodes
// of each node of a graph
HashMap> G = new HashMap<>();
// Traverse Edges[][2] array
for(int i = 0; i < M; i++)
{
if (G.containsKey(Edges[i][0]))
{
Set temp = G.get(Edges[i][0]);
temp.add(Edges[i][1]);
G.put(Edges[i][0], temp);
}
else
{
Set temp = new HashSet<>();
temp.add(Edges[i][1]);
G.put(Edges[i][0], temp);
}
}
// Check if a node is already visited or not
HashMap vis = new HashMap<>();
LexiDFS(G, S, vis);
}
// Driver code
public static void main(String[] args)
{
int N = 10, M = 10;
char S = 'a';
char[][] Edges = { { 'a', 'y' }, { 'a', 'z' },
{ 'a', 'p' }, { 'p', 'c' },
{ 'p', 'b' }, { 'y', 'm' },
{ 'y', 'l' }, { 'z', 'h' },
{ 'z', 'g' }, { 'z', 'i' } };
// Function Call
CreateGraph(N, M, S, Edges);
}
}
// This code is contributed by hritikrommie
Python3
# Python3 program for the above approach
G = [[] for i in range(300)]
vis = [0 for i in range(300)]
# Function to traverse the graph in
# lexicographical order using DFS
def LexiDFS(S):
global G, vis
# Mark S as visited nodes
vis[ord(S)] = 1
# Prvalue of visited nodes
print (S,end=" ")
# Traverse all adjacent nodes of S
for i in G[ord(S)]:
# If i is not visited
if (not vis[i]):
# Traverse all the nodes
# which is connected to i
LexiDFS(chr(i))
# Utility Function to traverse graph
# in lexicographical order of nodes
def CreateGraph(N, M, S, Edges):
global G
# Store all the adjacent nodes
# of each node of a graph
# Traverse Edges[][2] array
for i in Edges:
# Add the edges
G[ord(i[0])].append(ord(i[1]))
G[ord(i[0])] = sorted(G[ord(i[0])])
# Function Call
LexiDFS(S)
# Driver Code
if __name__ == '__main__':
N = 10
M = 10
S = 'a'
Edges=[ ['a', 'y' ],[ 'a', 'z' ],
[ 'a', 'p' ],[ 'p', 'c' ],
[ 'p', 'b' ],[ 'y', 'm' ],
[ 'y', 'l' ],[ 'z', 'h' ],
[ 'z', 'g' ],[ 'z', 'i' ] ]
# Function Call
CreateGraph(N, M, S, Edges);
# This code is contributed by mohitkumar29.
Javascript
a p b c y l m z g h i
时间复杂度: O(N * log(N))
辅助空间: O(N)
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