如何返回递归函数中的最后一个值?

您没有更新的值 heir 变量,用于存储函数调用的返回值 findHeir(node, heir) 。您需要一个简单的调整:

if (node.leftChild != null && node.rightChild != null) {
                int heir = 0;
                heir = findHeir(node, heir);
                System.out.println("Final node value: " + node.data);
                System.out.println("Final heir value: " + heir + " (should be 19)");
                //TODO add code to switch heir and node.data and delete node
            }

我们将把你的代码放在重症监护室。。。

In 节点 我们删除 钥匙 属性,以及实例化 left儿童 和 right孩子 因为它们是多余的。

class Node {    
   int data;
   Node leftChild;
   Node rightChild;

   Node( int data ) {
      this.data = data;
   }
}


public Node insertNode( Node node, int data ) {

     // we declare the new "Node"
   Node aux;
   if( node == null ) {
      aux = new Node( data );
      root = aux;
   }
   else if( data <= node.data ) {
        // if the left node does not exist, we assign "aux" to it
      if( node.leftChild == null ) {
           // we create
         aux = new Node( data );
         node.leftChild = aux;
      }
        // if exist, we recursion, passing it as a parameter
      else
         insertNode( node.leftChild, data );
   }
   else if( data > node.data ) {
      if( node.rightChild == null ) {
         aux = new Node( data );
         node.rightChild = aux;
      }
      else
         insertNode( node.rightChild, data );
   }
   return aux;
}

  // We move the "main" code here, so we avoid declaring static attributes and methods... 
  // and ugly ones :)
void init() {
   int[] treeNodes = { 5, 2, 12, -4, 3, 9, 21, 19, 25 };

     // we create the "root" node
   Node root = new Node( treeNodes[ 0 ]);

     // we create the others nodes
   for( int i = 1; i < treeNodes.length; i ++ ) {
      insertNode( root, treeNodes[ i ] );
   }
   System.out.println();

   for( int value : treeNodes ) 
      System.out.println( findHeir( root, value ));

   int key = 12;
   delete( root, key );
}

public static void main( String[] args ) {
   new Main().init();
}

所有的代码在一起。。。

public class Main {

   class Node {

      int data;
      Node leftChild;
      Node rightChild;

      Node( int data ) {
         this.data = data;
      }
   }

   Node root;

   public Node insertNode( Node node, int data ) {
      Node aux;
      if( node == null ) {             
         aux = new Node( data );
         root = aux;
      }
      else if( data <= node.data ) {
         if( node.leftChild == null ) {
            aux = new Node( data );
            node.leftChild = aux;
         }
         else {
            insertNode( node.leftChild, data );
         }
      }
      else if( data > node.data ) {
         if( node.rightChild == null ) {
            aux = new Node( data );
            node.rightChild = aux;
         }
         else {
            insertNode( node.rightChild, data );
         }
      }
      return aux;
   }

   //Method that returns 0 instead of 19
   public int findHeir( Node node, int heir ) {
      System.out.println( "Loop" );
      if( node.rightChild != null && node.leftChild != null ) {
         heir = node.leftChild.data;
         System.out.print( "Current node: " + node.rightChild.data );
         System.out.println( " Current heir: " + heir );
         return findHeir( node.rightChild, heir );
      }
      else if( node.rightChild == null ) {
         System.out.println( "Heir value before return: " + heir );
         return heir;
      }
      return heir;
   }

   //Deletes the node
   public Node delete( Node node, int data ) {
      //Checks if the node exists
      if( node == null ) {
         System.out.println( "The node you entered does not exist." );
         return node;
      }
      //Looks for the correct node
      else if( data < node.data ) {
         System.out.println( "  es menor que " + node.data );
         node.leftChild = delete( node.leftChild, data );
      }
      else if( data > node.data ) {
         System.out.println( "  es mayor que " + node.data );
         //node.rightChild = 
         System.out.println( " derche = " + node.rightChild.data );
         delete( node.rightChild, data );
      }
      //Found the correct node
      else {
         //Delete node if it has 2 children
         if( node.leftChild != null && node.rightChild != null ) {
            int heir = 0;
            findHeir( node, heir );
            System.out.println( "Final node value: " + node.data );
            System.out.println( "Final heir value: " + heir + " (should be 19)" );
            //TODO add code to switch heir and node.data and delete node
         }
      }
      return node;
   }

   void init() {
      int[] treeNodes = { 5, 2, 12, -4, 3, 9, 21, 19, 25 };
      Node root = new Node( treeNodes[ 0 ] );
      for( int i = 1; i < treeNodes.length; i ++ ) {
         insertNode( root, treeNodes[ i ] );
      }
      System.out.println();

      for( int value : treeNodes ) {
         System.out.println( findHeir( root, value ) );
      }

      int key = 12;
      delete( root, key );
   }

   public static void main( String[] args ) {
      new Main().init();
   }
}