Java中二叉树的建立和各种遍历实例代码

PreOrder: GDAFEMHZ 
InOrder: ADEFGHMZ 
PostOrder: AEFDHZMG

class Tree{
	char val;
	Tree left;
	Tree right;
	Tree(char val, Tree left, Tree right){
		this.val = val;
		this.left = left;
		this.right = right;
	}
	Tree(){
	}
	Tree(char val){
		this.val = val;
		this.left = null;
		this.right =null;
	}
}

public static Tree buildTree(char[] preOrder, char[] inOrder){
	//preOrder是先序序列
	//inOrder是中序序列
	if(preOrder == null || preOrder.length == 0){
		return null;
	}
	Tree root = new Tree(preOrder[0]);
	//找到inOrder中的root的位置
	int inOrderIndex = 0;
	for (char i = 0; i < inOrder.length; i++){
		if(inOrder[i] == root.val){
			inOrderIndex = i;
		}
	}
	//preOrder的左子树和右子树部分
	char[] preOrderLeft = Arrays.copyOfRange(preOrder, 1, 1+inOrderIndex);
	char[] preOrderRight = Arrays.copyOfRange(preOrder, 1+inOrderIndex, preOrder.length);
	//inOrder的左子树和右子树部分
	char[] inOrderLeft = Arrays.copyOfRange(inOrder, 0, inOrderIndex);
	char[] inOrderRight = Arrays.copyOfRange(inOrder, inOrderIndex+1, inOrder.length);
	//递归建立左子树和右子树
	Tree leftChild = buildTree(preOrderLeft, inOrderLeft);
	Tree rightChild = buildTree(preOrderRight, inOrderRight);
	root.left = leftChild;
	root.right = rightChild;
	return root;
}

public static void postOrderPrint(Tree root){
    //后续遍历
    //左右根
    if(root.left != null){
      postOrderPrint(root.left);
    }
    if(root.right != null){
      postOrderPrint(root.right);
    }
    System.out.print(root.val + " ");
  }

public static void layerOrderPrint(Tree root){
    if(root == null){
      return;
    }
    //层序遍历
    Queue<Tree> qe = new LinkedList<Tree>();
    qe.add(root);
    while(!qe.isEmpty()){
      Tree node = qe.poll();
      System.out.print(node.val + " ");
      if(node.left != null){
        qe.add(node.left);
      }
      if(node.right != null){
        qe.add(node.right);
      }
    }
  }

public static void deepFirstPrint(Tree root){
    //深度优先遍历等价于先序遍历
    //所以可以直接使用先序遍历
    if(root == null){
      return;
    }
    System.out.print(root.val + " ");
    if(root.left != null){
      deepFirstPrint(root.left);
    }
    if(root.right != null){
      deepFirstPrint(root.right);
    }
  }

public static void deepFirstPrintNoneRec(Tree root){
    //深度优先遍历的非递归形式
    if(root == null){
      return;
    }
    Stack<Tree> st = new Stack<Tree>();
    st.add(root);
    while(!st.isEmpty()){
      Tree node = st.pop();
      System.out.print(node.val + " ");
      //栈是后进先出的
      //先加右孩子后加左孩子
      if(node.right != null){
        st.add(node.right);
      }
      if(node.left != null){
        st.add(node.left);
      }
    }
  }

public static void main(String[] args) {
    char[] preOrder = "GDAFEMHZ".toCharArray();
    char[] inOrder = "ADEFGHMZ".toCharArray();
    Tree root = Main.buildTree(preOrder, inOrder);
//   Main.postOrderPrint(root); //后序遍历
//   Main.layerOrderPrint(root); //层序遍历
//   Main.deepFirstPrint(root); //深度优先遍历
//   Main.deepFirstPrintNoneRec(root); //深度优先遍历的非递归版本
  }