Java program to find the smallest element in a tree

In the following example of Java program to find the smallest element in a binary tree :

Program :

public class SmallestNode {  
      //Represent the node of binary tree  
      public static class Node{  
        int data;  
        Node left;  
        Node right;  
  
        public Node(int data){  
            //Assign data to the new node, set left and right children to null  
            this.data = data;  
            this.left = null;  
            this.right = null;  
        }  
      }  
  
      //Represent the root of binary tree  
      public Node root;  
  
      public SmallestNode(){  
          root = null;  
      }  
  
      //smallestElement() will find out the smallest node in the binary tree  
      public int smallestElement(Node temp){  
          //Check whether tree is empty  
          if(root == null) {  
              System.out.println("Tree is empty");  
              return 0;  
          }  
          else {  
                int leftMin, rightMin;  
                //Min will store temp's data  
                int min = temp.data;  
  
                //It will find smallest element in left subtree  
                if(temp.left != null){  
                  leftMin = smallestElement(temp.left);  
                  //If min is greater than leftMin then store the value of leftMin into min  
                  min = Math.min(min, leftMin);  
                }  
  
                //It will find smallest element in right subtree  
                if(temp.right != null){  
                  rightMin = smallestElement(temp.right);  
                  //If min is greater than rightMin then store the value of rightMin into min  
                  min = Math.min(min, rightMin);  
                }  
                return min;  
          }  
      }  
  
      public static void main(String[] args) {  
  
        SmallestNode bt = new SmallestNode();  
        //Add nodes to the binary tree  
        bt.root = new Node(4);  
        bt.root.left = new Node(2);  
        bt.root.right = new Node(3);  
        bt.root.left.left = new Node(1);  
        bt.root.right.left = new Node(5);  
        bt.root.right.right = new Node(6);  
  
        //Display smallest node in the binary tree  
        System.out.println("Smallest element in the binary tree: " + bt.smallestElement(bt.root));  
      }  
}

Output :

Smallest element in the binary tree: 1

In the above program, we will find out the smallest node in the given binary tree. We first define variable min that will hold root's data. Then, we traverse through left sub-tree to find the smallest node in left subtree. Compare it with min and store minimum of two in variable min. Then, we traverse through right subtree to find smallest node and compare it with min. At the end, min will have the smallest node.

represents a binary tree. Initially, min will hold 4. Recursive through left subtree.

1. min = 4, leftMin = 2    =>  (2 < 4) then min = 2  
2. min = 2, leftMin = 1    =>  (1 < 2) then min = 1  â€‹

Recursive through right subtree.

1. min = 1, rightMin = 3  =>  (1 < 3) then min = 1   â€‹
2. Recurse in left subtree of 5   
3. min = 1, leftMin = 5    =>  (1 < 5) then min = 1  â€‹

Recurse in right subtree of 3

1. min = 1, rightMin = 6  =>  (1 < 6) then min = 1  â€‹

So, smallest node in above binary tree is 1.