[面试备忘]求二叉树中节点最大距离 & 分层遍历二叉树

编程之美3.8-求二叉树中节点最大距离

编程之美3.10分层遍历二叉树

#include <iostream>
#include <vector>
#include <cstring>
#include "general.h"


//编程之美3.8-求二叉树中节点最大距离-递归
int getMaxDepth(CPTNODE pNode) //求最大深度
{
    if (pNode == NULL) {
        return -1;
    }
    return 1 + MAX(getMaxDepth(pNode->left), getMaxDepth(pNode->right));
}

int getMaxDistance(CPTNODE pNode)//求最大点距离
{
    if (pNode == NULL) {
        return 0;
    }
    return MAX(MAX(getMaxDistance(pNode->left), getMaxDistance(pNode->right)), 
           2 +  getMaxDepth(pNode->left) + getMaxDepth(pNode->right));
}

//分层遍历二叉树-普通方法
bool printNDepthNode(CPTNODE root, int length) 
{
    if (root == NULL) {
        return false;
    }
    if (length == 0) {
        std::cout << root->value << ' ';
        return true;
    }
    return printNDepthNode(root->left, length - 1) + //not "||", shortcut! 
           printNDepthNode(root->right, length - 1);
}

void printNodeByDepth(CPTNODE root)
{
    int depth = 0;
    while(printNDepthNode(root, depth++)) {
        std::cout << std::endl;
    }    
}

//分层遍历改进方法
void printNodeByDepthNew(CPTNODE root)
{
    if (root == NULL) {
        return;
    }
    std::vector<CPTNODE> nodeVec;
    nodeVec.push_back(root);
    unsigned startFlag = 0;
    unsigned depthFlag = nodeVec.size();
    while (startFlag != nodeVec.size()) {
        if (nodeVec[startFlag]->left != NULL) {
            nodeVec.push_back(nodeVec[startFlag]->left);
        }
        if (nodeVec[startFlag]->right != NULL) {
            nodeVec.push_back(nodeVec[startFlag]->right);
        }
        std::cout << nodeVec[startFlag]->value << ' ' << std::flush;
        if (++startFlag == depthFlag) {
            std::cout << std::endl;
            depthFlag = nodeVec.size();
        }
    }
}
    
int main()
{
    char preOrder[] = "124853697";
    char inOrder[] = "842516937";
    PTNODE root = NULL;
    buildBinaryTree(preOrder, inOrder, strlen(preOrder), root);
    std::cout << "Max Distance: " << getMaxDistance(root) << std::endl;
    printNodeByDepth(root);
    printNodeByDepthNew(root);
    return 0;
}

分层遍历二叉树，如果想要从深层到浅层遍历，递归方法：先求二叉树深度，然后递减打印。

改进方法，先从浅到深分层将二叉树内数据压入数组，并记录每次分层边界下标，然后倒序打印。

如果即要从深到浅，而且从右到左，将数组倒序，然后正常打印。