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📜  BST中最大小于或等于N的数字(迭代方法)

📅  最后修改于: 2021-05-24 21:22:40             🧑  作者: Mango

我们有一个二进制搜索树和一个数字N。我们的任务是在二进制搜索树中找到小于或等于N的最大数字。如果元素存在,则打印该元素的值,否则打印-1。

BST

示例:对于上述给定的二进制搜索树,

Input : N = 24
Output :result = 21
(searching for 24 will be like-5->12->21)

Input  : N = 4
Output : result = 3
(searching for 4 will be like-5->2->3)

我们在下面的文章中讨论了递归方法。
BST中最大的数字,小于或等于N
这里讨论一种迭代方法。我们试图找到目标的前身。保留两个指针,一个指向当前节点,另一个用于存储答案。如果当前节点的数据> N,则向左移动。在其他情况下,当当前节点的数据小于N时,当前节点可以作为我们的答案(到目前为止),并且我们向右移动。

C++
// C++ code to find the largest value smaller
// than or equal to N
#include 
using namespace std;
  
struct Node {
    int key;
    Node *left, *right;
};
  
// To create new BST Node
Node* newNode(int item)
{
    Node* temp = new Node;
    temp->key = item;
    temp->left = temp->right = NULL;
    return temp;
}
  
// To insert a new node in BST
Node* insert(Node* node, int key)
{
    // if tree is empty return new node
    if (node == NULL)
        return newNode(key);
  
    // if key is less then or grater then
    // node value then recur down the tree
    if (key < node->key)
        node->left = insert(node->left, key);
    else if (key > node->key)
        node->right = insert(node->right, key);
  
    // return the (unchanged) node pointer
    return node;
}
  
// Returns largest value smaller than or equal to
// key. If key is smaller than the smallest, it 
// returns -1.
int findFloor(Node* root, int key)
{
    Node *curr = root, *ans = NULL;
    while (curr) {
        if (curr->key <= key) {
            ans = curr;
            curr = curr->right;
        }
        else
            curr = curr->left;
    }
    if (ans)
        return ans->key;
    return -1;
}
  
// Driver code
int main()
{
    int N = 25;
  
    Node* root = insert(root, 19);
    insert(root, 2);
    insert(root, 1);
    insert(root, 3);
    insert(root, 12);
    insert(root, 9);
    insert(root, 21);
    insert(root, 19);
    insert(root, 25);
  
    printf("%d", findFloor(root, N));
  
    return 0;
}


Java
// Java code to find the largest value smaller 
// than or equal to N 
class GFG
{
      
static class Node
{ 
    int key; 
    Node left, right; 
}; 
  
// To create new BST Node 
static Node newNode(int item) 
{ 
    Node temp = new Node(); 
    temp.key = item; 
    temp.left = temp.right = null; 
    return temp; 
} 
  
// To insert a new node in BST 
static Node insert(Node node, int key) 
{ 
    // if tree is empty return new node 
    if (node == null) 
        return newNode(key); 
  
    // if key is less then or grater then 
    // node value then recur down the tree 
    if (key < node.key) 
        node.left = insert(node.left, key); 
    else if (key > node.key) 
        node.right = insert(node.right, key); 
  
    // return the (unchanged) node pointer 
    return node; 
} 
  
// Returns largest value smaller than or equal to 
// key. If key is smaller than the smallest, it 
// returns -1. 
static int findFloor(Node root, int key) 
{ 
    Node curr = root, ans = null; 
    while (curr != null) 
    { 
        if (curr.key <= key)
        { 
            ans = curr; 
            curr = curr.right; 
        } 
        else
            curr = curr.left; 
    } 
    if (ans != null) 
        return ans.key; 
    return -1; 
} 
  
// Driver code 
public static void main(String[] args) 
{
    int N = 25; 
  
    Node root = new Node();
    insert(root, 19); 
    insert(root, 2); 
    insert(root, 1); 
    insert(root, 3); 
    insert(root, 12); 
    insert(root, 9); 
    insert(root, 21); 
    insert(root, 19); 
    insert(root, 25); 
  
    System.out.printf("%d", findFloor(root, N)); 
}
}
  
/* This code is contributed by PrinciRaj1992 */


Python3
# Python3 code to find the largest value 
# smaller than or equal to N
  
class newNode:
      
    def __init__(self, item):
          
        self.key = item
        self.left = None
        self.right = None
  
# To insert a new node in BST
def insert(node, key):
      
    # If tree is empty return new node
    if (node == None):
        return newNode(key)
  
    # If key is less then or grater then
    # node value then recur down the tree
    if (key < node.key):
        node.left = insert(node.left, key)
    elif (key > node.key):
        node.right = insert(node.right, key)
  
    # Return the (unchanged) node pointer
    return node
  
# Returns largest value smaller than or 
# equal to key. If key is smaller than
# the smallest, it returns -1.
def findFloor(root, key):
      
    curr = root
    ans = None
      
    while (curr):
        if (curr.key <= key):
            ans = curr
            curr = curr.right
        else:
            curr = curr.left
    if (ans):
        return ans.key
          
    return -1
  
# Driver code
if __name__ == '__main__':
      
    N = 25
    root = None
  
    root = insert(root, 19)
    insert(root, 2)
    insert(root, 1)
    insert(root, 3)
    insert(root, 12)
    insert(root, 9)
    insert(root, 21)
    insert(root, 19)
    insert(root, 25)
  
    print(findFloor(root, N))
  
# This code is contributed by bgangwar59


C#
// C# code to find the largest value smaller 
// than or equal to N 
using System;
using System.Collections.Generic; 
      
class GFG
{
      
public class Node
{ 
    public int key; 
    public Node left, right; 
}; 
  
// To create new BST Node 
static Node newNode(int item) 
{ 
    Node temp = new Node(); 
    temp.key = item; 
    temp.left = temp.right = null; 
    return temp; 
} 
  
// To insert a new node in BST 
static Node insert(Node node, int key) 
{ 
    // if tree is empty return new node 
    if (node == null) 
        return newNode(key); 
  
    // if key is less then or grater then 
    // node value then recur down the tree 
    if (key < node.key) 
        node.left = insert(node.left, key); 
    else if (key > node.key) 
        node.right = insert(node.right, key); 
  
    // return the (unchanged) node pointer 
    return node; 
} 
  
// Returns largest value smaller than or equal to 
// key. If key is smaller than the smallest, it 
// returns -1. 
static int findFloor(Node root, int key) 
{ 
    Node curr = root, ans = null; 
    while (curr != null) 
    { 
        if (curr.key <= key)
        { 
            ans = curr; 
            curr = curr.right; 
        } 
        else
            curr = curr.left; 
    } 
    if (ans != null) 
        return ans.key; 
    return -1; 
} 
  
// Driver code 
public static void Main(String[] args) 
{
    int N = 25; 
  
    Node root = new Node();
    insert(root, 19); 
    insert(root, 2); 
    insert(root, 1); 
    insert(root, 3); 
    insert(root, 12); 
    insert(root, 9); 
    insert(root, 21); 
    insert(root, 19); 
    insert(root, 25); 
  
    Console.Write("{0}", findFloor(root, N)); 
}
}
  
// This code is contributed by Rajput-Ji


输出:

25