smallest_element_in_a_tree.java

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));  
      }  
}