打印级别订单二进制搜索树格式

Question

我已实现以下代码以按级别顺序打印二叉搜索树.

public void printLevelOrder(int depth) {
    for (int i = 1; i <= depth; i++) {
        printLevel(root, i);
    }
}

public void printLevel(BinaryNode<AnyType> t, int level) {
    if (t == null) {
        return;
    }
    if (level == 1) {
        System.out.print(t.element);
    } else if (level > 1) {
        printLevel(t.left, level - 1);
        printLevel(t.right, level - 1);
    }
}

我试图弄清楚如何改进我的代码,让它以某种格式打印出来.

举个例子,给一棵树

    1 
   / \
  2   3
 /   / \
4   5   6

目前它打印如下:

123456

我正在寻找它打印如下:

Level 0: 1
Level 1: 2 3
Level 2: 4 5 6

Answer 1

不是在递归函数调用内立即打印值,而是使用字符串来保存值.这样可以更容易地操作输出.

public void printLevelOrder(int depth) {
    for (int i = 1; i <= depth; i++) {
        System.out.print("Level " + (i-1) + ": ");
        String levelNodes = printLevel(root, i);
        System.out.print(levelNodes + "\n");
    }
}

public String printLevel(BinaryNode<AnyType> t, int level) {
    if (t == null) {
        return "";
    }
    if (level == 1) {
        return t.element + " ";
    } else if (level > 1) {
        String leftStr = printLevel(t.left, level - 1);
        String rightStr = printLevel(t.right, level - 1);
        return leftStr + rightStr;
    }
    else // you need this to get it to compile
      return "";
}

输出:

Level 0: 1 
Level 1: 2 3 
Level 2: 4 5 6