Java 遍历二叉树

Binary.java

import java.util.Stack;

public class BinaryTree {
protected Node root;

public BinaryTree(Node root) {
   this.root = root;
}

public Node getRoot() {
   return root;
}

/** 构造树 */
public static Node init() {
   Node a = new Node('A');
   Node b = new Node('B', null, a);
   Node c = new Node('C');
   Node d = new Node('D', b, c);
   Node e = new Node('E');
   Node f = new Node('F', e, null);
   Node g = new Node('G', null, f);
   Node h = new Node('H', d, g);
   return h;// root
}

/** 访问节点 */
public static void visit(Node p) {
   System.out.print(p.getKey() + " ");
}

/** 递归实现前序遍历 */
protected static void preorder(Node p) {
   if (p != null) {
    visit(p);
    preorder(p.getLeft());
    preorder(p.getRight());
   }
}

/** 递归实现中序遍历 */
protected static void inorder(Node p) {
   if (p != null) {
    inorder(p.getLeft());
    visit(p);
    inorder(p.getRight());
   }
}

/** 递归实现后序遍历 */
protected static void postorder(Node p) {
   if (p != null) {
    postorder(p.getLeft());
    postorder(p.getRight());
    visit(p);
   }
}

/** 非递归实现前序遍历 */
protected static void iterativePreorder(Node p) {
   Stack<Node> stack = new Stack<Node>();
   if (p != null) {
    stack.push(p);
    while (!stack.empty()) {
     p = stack.pop();
     visit(p);
     if (p.getRight() != null)
      stack.push(p.getRight());
     if (p.getLeft() != null)
      stack.push(p.getLeft());
    }
   }
}

/** 非递归实现前序遍历2 */
protected static void iterativePreorder2(Node p) {
   Stack<Node> stack = new Stack<Node>();
   Node node = p;
   while (node != null || stack.size() > 0) {
    while (node != null) {//压入所有的左节点，压入前访问它
     visit(node);
     stack.push(node);
     node = node.getLeft();
    }
    if (stack.size() > 0) {//
     node = stack.pop();
     node = node.getRight();
    }
   }
}

/** 非递归实现后序遍历 */
protected static void iterativePostorder(Node p) {
   Node q = p;
   Stack<Node> stack = new Stack<Node>();
   while (p != null) {
    // 左子树入栈
    for (; p.getLeft() != null; p = p.getLeft())
     stack.push(p);
    // 当前节点无右子或右子已经输出
    while (p != null && (p.getRight() == null || p.getRight() == q)) {
     visit(p);
     q = p;// 记录上一个已输出节点
     if (stack.empty())
      return;
     p = stack.pop();
    }
    // 处理右子
    stack.push(p);
    p = p.getRight();
   }
}

/** 非递归实现后序遍历 双栈法 */
protected static void iterativePostorder2(Node p) {
   Stack<Node> lstack = new Stack<Node>();
   Stack<Node> rstack = new Stack<Node>();
   Node node = p, right;
   do {
    while (node != null) {
     right = node.getRight();
     lstack.push(node);
     rstack.push(right);
     node = node.getLeft();
    }
    node = lstack.pop();
    right = rstack.pop();
    if (right == null) {
     visit(node);
    } else {
     lstack.push(node);
     rstack.push(null);
    }
    node = right;
   } while (lstack.size() > 0 || rstack.size() > 0);
}

/** 非递归实现后序遍历 单栈法*/
protected static void iterativePostorder3(Node p) {
   Stack<Node> stack = new Stack<Node>();
   Node node = p, prev = p;
   while (node != null || stack.size() > 0) {
    while (node != null) {
     stack.push(node);
     node = node.getLeft();
    }
    if (stack.size() > 0) {
     Node temp = stack.peek().getRight();
     if (temp == null || temp == prev) {
      node = stack.pop();
      visit(node);
      prev = node;
      node = null;
     } else {
      node = temp;
     }
    }

   }
}

/** 非递归实现后序遍历4 双栈法*/
protected static void iterativePostorder4(Node p) {
   Stack<Node> stack = new Stack<Node>();
   Stack<Node> temp = new Stack<Node>();
   Node node = p;
   while (node != null || stack.size() > 0) {
    while (node != null) {
     temp.push(node);
     stack.push(node);
     node = node.getRight();
    }
    if (stack.size() > 0) {
     node = stack.pop();
     node = node.getLeft();
    }
   }
   while (temp.size() > 0) {
    node = temp.pop();
    visit(node);
   }
}

/** 非递归实现中序遍历 */
protected static void iterativeInorder(Node p) {
   Stack<Node> stack = new Stack<Node>();
   while (p != null) {
    while (p != null) {
     if (p.getRight() != null)
      stack.push(p.getRight());// 当前节点右子入栈
     stack.push(p);// 当前节点入栈
     p = p.getLeft();
    }
    p = stack.pop();
    while (!stack.empty() && p.getRight() == null) {
     visit(p);
     p = stack.pop();
    }
    visit(p);
    if (!stack.empty())
     p = stack.pop();
    else
     p = null;
   }
}

/** 非递归实现中序遍历2 */
protected static void iterativeInorder2(Node p) {
   Stack<Node> stack = new Stack<Node>();
   Node node = p;
   while (node != null || stack.size() > 0) {
    while (node != null) {
     stack.push(node);
     node = node.getLeft();
    }
    if (stack.size() > 0) {
     node = stack.pop();
     visit(node);
     node = node.getRight();
    }
   }
}

/**
* @param args
*/
public static void main(String[] args) {
   BinaryTree tree = new BinaryTree(init());
   System.out.print(" Pre-Order:");
   preorder(tree.getRoot());
   System.out.println();
   System.out.print(" In-Order:");
   inorder(tree.getRoot());
   System.out.println();
   System.out.print("Post-Order:");
   postorder(tree.getRoot());
   System.out.println();
   System.out.print(" Pre-Order:");
   iterativePreorder(tree.getRoot());
   System.out.println();
   System.out.print("Pre-Order2:");
   iterativePreorder2(tree.getRoot());
   System.out.println();
   System.out.print(" In-Order:");
   iterativeInorder(tree.getRoot());
   System.out.println();
   System.out.print(" In-Order2:");
   iterativeInorder2(tree.getRoot());
   System.out.println();
   System.out.print(" Post-Order:");
   iterativePostorder(tree.getRoot());
   System.out.println();
   System.out.print("Post-Order2:");
   iterativePostorder2(tree.getRoot());
   System.out.println();
   System.out.print("Post-Order3:");
   iterativePostorder3(tree.getRoot());
   System.out.println();
   System.out.print("Post-Order4:");
   iterativePostorder4(tree.getRoot());
   System.out.println();

}

}

 

Node.java

public class Node {
private char key;
private Node left, right;

public Node(char key) {
   this(key, null, null);
}

public Node(char key, Node left, Node right) {
   this.key = key;
   this.left = left;
   this.right = right;
}

public char getKey() {
   return key;
}

public void setKey(char key) {
   this.key = key;
}

public Node getLeft() {
   return left;
}

public void setLeft(Node left) {
   this.left = left;
}

public Node getRight() {
   return right;
}

public void setRight(Node right) {
   this.right = right;
}
}