打印二叉树中第一个最短的根到叶子的路径
原文：https://www.geeksforgeeks.org/print-the-first-shortest-root-to-leaf-path-in-a-binary-tree/
给定具有不同值的二叉树，任务是打印第一个最小的根到叶路径。 我们基本上需要打印出节点数最少的最左边的根到叶的路径。
Input:
1
/ \
2 3
/ / \
4 5 7
/ \ \
10 11 8
Output: 1 3 5
Input:
1
/ \
2 3
/ / \
40 5 7
\
8
Output: 1 2 40
方法：这个想法是使用队列执行层次顺序遍历，即映射parent来存储将出现在最短路径中的节点。 使用层次顺序遍历，我们找到最左边的叶子。 找到最左边的叶子后，便使用映射打印路径。
下面是上述方法的实现：
C++
// C++ program to print first shortest
// root to leaf path
#include <bits/stdc++.h>
using namespace std;
// Binary tree node
struct Node {
struct Node* left;
struct Node* right;
int data;
};
// Function to create a new
// Binary node
struct Node* newNode(int data)
{
struct Node* temp = new Node;
temp->data = data;
temp->left = NULL;
temp->right = NULL;
return temp;
}
// Recursive function used by leftMostShortest
// to print the first shortest root to leaf path
void printPath(int Data, unordered_map<int,
int> parent)
{
// If the root's data is same as
// its parent data then return
if (parent[Data] == Data)
return;
// Recur for the function printPath
printPath(parent[Data], parent);
// Print the parent node's data
cout << parent[Data] << " ";
}
// Function to perform level order traversal
// until we find the first leaf node
void leftMostShortest(struct Node* root)
{
// Queue to store the nodes
queue<struct Node*> q;
// Push the root node
q.push(root);
// Initialize the value of first
// leaf node to occur as -1
int LeafData = -1;
// To store the current node
struct Node* temp = NULL;
// Map to store the parent node's data
unordered_map<int, int> parent;
// Parent of root data is set as it's
// own value
parent[root->data] = root->data;
// We store first node of the smallest level
while (!q.empty()) {
temp = q.front();
q.pop();
// If the first leaf node has been found
// set the flag variable as 1
if (!temp->left && !temp->right) {
LeafData = temp->data;
break;
}
else {
// If current node has left
// child, push in the queue
if (temp->left) {
q.push(temp->left);
// Set temp's left node's parent as temp
parent[temp->left->data] = temp->data;
}
// If current node has right
// child, push in the queue
if (temp->right) {
q.push(temp->right);
// Set temp's right node's parent
// as temp
parent[temp->right->data] = temp->data;
}
}
}
// Recursive function to print the first
// shortest root to leaf path
printPath(LeafData, parent);
// Print the leaf node of the first
// shortest path
cout << LeafData << " ";
}
// Driver code
int main()
{
struct Node* root = newNode(1);
root->left = newNode(2);
root->right = newNode(3);
root->left->left = newNode(4);
root->right->left = newNode(5);
root->right->right = newNode(7);
root->left->left->left = newNode(10);
root->left->left->right = newNode(11);
root->right->right->left = newNode(8);
leftMostShortest(root);
return 0;
}
Java
// Java program to print first shortest
// root to leaf path
import java.util.*;
class GFG{
// Binary tree node
static class Node
{
Node left;
Node right;
int data;
};
// Function to create a new
// Binary node
static Node newNode(int data)
{
Node temp = new Node();
temp.data = data;
temp.left = null;
temp.right = null;
return temp;
}
// Recursive function used by leftMostShortest
// to print the first shortest root to leaf path
static void printPath(int Data,
HashMap<Integer,
Integer> parent)
{
// If the root's data is same as
// its parent data then return
if (parent.get(Data) == Data)
return;
// Recur for the function printPath
printPath(parent.get(Data), parent);
// Print the parent node's data
System.out.print(parent.get(Data) + " ");
}
// Function to perform level order traversal
// until we find the first leaf node
static void leftMostShortest(Node root)
{
// Queue to store the nodes
Queue<Node> q = new LinkedList<>();
// Add the root node
q.add(root);
// Initialize the value of first
// leaf node to occur as -1
int LeafData = -1;
// To store the current node
Node temp = null;
// Map to store the parent node's data
HashMap<Integer,
Integer> parent = new HashMap<>();
// Parent of root data is set as it's
// own value
parent.put(root.data, root.data);
// We store first node of the smallest level
while (!q.isEmpty())
{
temp = q.poll();
// If the first leaf node has been found
// set the flag variable as 1
if (temp.left == null &&
temp.right == null)
{
LeafData = temp.data;
break;
}
else
{
// If current node has left
// child, add in the queue
if (temp.left != null)
{
q.add(temp.left);
// Set temp's left node's parent
// as temp
parent.put(temp.left.data,
temp.data);
}
// If current node has right
// child, add in the queue
if (temp.right != null)
{
q.add(temp.right);
// Set temp's right node's parent
// as temp
parent.put(temp.right.data,
temp.data);
}
}
}
// Recursive function to print the
// first shortest root to leaf path
printPath(LeafData, parent);
// Print the leaf node of the first
// shortest path
System.out.println(LeafData + " ");
}
// Driver Code
public static void main(String[] args)
{
Node root = newNode(1);
root.left = newNode(2);
root.right = newNode(3);
root.left.left = newNode(4);
root.right.left = newNode(5);
root.right.right = newNode(7);
root.left.left.left = newNode(10);
root.left.left.right = newNode(11);
root.right.right.left = newNode(8);
leftMostShortest(root);
}
}
// This code is contributed by sanjeev2552
Python3
# Python3 program to print first
# shortest root to leaf path
# Binary tree node
class Node:
def __init__(self, data):
self.data = data
self.left = None
self.right = None
# Recursive function used by leftMostShortest
# to print the first shortest root to leaf path
def printPath(Data, parent):
# If the root's data is same as
# its parent data then return
if parent[Data] == Data:
return
# Recur for the function printPath
printPath(parent[Data], parent)
# Print the parent node's data
print(parent[Data], end = " ")
# Function to perform level order traversal
# until we find the first leaf node
def leftMostShortest(root):
# Queue to store the nodes
q = []
# Push the root node
q.append(root)
# Initialize the value of first
# leaf node to occur as -1
LeafData = -1
# To store the current node
temp = None
# Map to store the parent node's data
parent = {}
# Parent of root data is set
# as it's own value
parent[root.data] = root.data
# We store first node of the
# smallest level
while len(q) != 0:
temp = q.pop(0)
# If the first leaf node has been
# found set the flag variable as 1
if not temp.left and not temp.right:
LeafData = temp.data
break
else:
# If current node has left
# child, push in the queue
if temp.left:
q.append(temp.left)
# Set temp's left node's parent as temp
parent[temp.left.data] = temp.data
# If current node has right
# child, push in the queue
if temp.right:
q.append(temp.right)
# Set temp's right node's parent
# as temp
parent[temp.right.data] = temp.data
# Recursive function to print the first
# shortest root to leaf path
printPath(LeafData, parent)
# Print the leaf node of the
# first shortest path
print(LeafData, end = " ")
# Driver code
if __name__ == "__main__":
root = Node(1)
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(4)
root.right.left = Node(5)
root.right.right = Node(7)
root.left.left.left = Node(10)
root.left.left.right = Node(11)
root.right.right.left = Node(8)
leftMostShortest(root)
# This code is contributed by Rituraj Jain
C
// C# program to print first shortest
// root to leaf path
using System;
using System.Collections;
using System.Collections.Generic;
class GFG{
// Binary tree node
public class Node
{
public Node left;
public Node right;
public int data;
};
// Function to create a new
// Binary node
public static Node newNode(int data)
{
Node temp = new Node();
temp.data = data;
temp.left = null;
temp.right = null;
return temp;
}
// Recursive function used by leftMostShortest
// to print the first shortest root to leaf path
static void printPath(int Data,
Dictionary<int, int> parent)
{
// If the root's data is same as
// its parent data then return
if (parent[Data] == Data)
return;
// Recur for the function printPath
printPath(parent[Data], parent);
// Print the parent node's data
Console.Write(parent[Data] + " ");
}
// Function to perform level order traversal
// until we find the first leaf node
static void leftMostShortest(Node root)
{
// Queue to store the nodes
Queue q = new Queue();
// Add the root node
q.Enqueue(root);
// Initialize the value of first
// leaf node to occur as -1
int LeafData = -1;
// To store the current node
Node temp = null;
// Map to store the parent node's data
Dictionary<int,
int> parent = new Dictionary<int,
int>();
// Parent of root data is set as it's
// own value
parent[root.data] = root.data;
// We store first node of the
// smallest level
while (q.Count != 0)
{
temp = (Node)q.Dequeue();
// If the first leaf node has been
// found set the flag variable as 1
if (temp.left == null &&
temp.right == null)
{
LeafData = temp.data;
break;
}
else
{
// If current node has left
// child, add in the queue
if (temp.left != null)
{
q.Enqueue(temp.left);
// Set temp's left node's parent
// as temp
parent[temp.left.data] = temp.data;
}
// If current node has right
// child, add in the queue
if (temp.right != null)
{
q.Enqueue(temp.right);
// Set temp's right node's parent
// as temp
parent[temp.right.data] = temp.data;
}
}
}
// Recursive function to print the
// first shortest root to leaf path
printPath(LeafData, parent);
// Print the leaf node of the first
// shortest path
Console.Write(LeafData + " ");
}
// Driver Code
public static void Main(string[] args)
{
Node root = newNode(1);
root.left = newNode(2);
root.right = newNode(3);
root.left.left = newNode(4);
root.right.left = newNode(5);
root.right.right = newNode(7);
root.left.left.left = newNode(10);
root.left.left.right = newNode(11);
root.right.right.left = newNode(8);
leftMostShortest(root);
}
}
// This code is contributed by rutvik_56
输出：
1 3 5
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