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。
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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 bgangwar59C#
// 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