PAT 1020. Tree Traversals (25)

1020. Tree Traversals (25)

Suppose that all the keys in a binary tree are distinct positive integers. Given the postorder and inorder traversal sequences, you are supposed to output the level order traversal sequence of the corresponding binary tree.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (<=30), the total number of nodes in the binary tree. The second line gives the postorder sequence and the third line gives the inorder sequence. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print in one line the level order traversal sequence of the corresponding binary tree. All the numbers in a line must be separated by exactly one space, and there must be no extra space at the end of the line.

Sample Input:

7
2 3 1 5 7 6 4
1 2 3 4 5 6 7

Sample Output:

4 1 6 3 5 7 2

#include <iostream>
#include <queue>

using namespace std;

struct Node
{
    int val;
    Node* left;
    Node* right;
    Node(){ val = 0; left = right = nullptr; }
};

static int postOrder[30];
static int inOrder[30];

int InOrderFindIndex(int val, int inLeft, int inRight)
{
    for (int i = inLeft; i < inRight; i++)
        if (inOrder[i] == val)
            return i;
}

Node* ConstructTree(int postLeft, int postRight, int inLeft, int inRight)
{
    if (postLeft == postRight)
        return nullptr;

    Node* root = new Node;
    root->val = postOrder[postRight-1];
    int index = InOrderFindIndex(root->val, inLeft, inRight);
    int leftLength = index - inLeft;
    int rightLength = inRight - index - 1;
    root->left = ConstructTree(postLeft, postLeft + leftLength, inLeft, index);
    root->right = ConstructTree(postLeft + leftLength, postRight - 1, index + 1, inRight);

    return root;
}

void LevelOrderTraversal(Node* root, int NodeNum)
{
    queue<Node*> que;
    que.push(root);
    int cnt = 0;
    while (!que.empty())
    {
        Node* last = que.front();
        que.pop();
        cout << last->val;
        ++cnt;
        if (cnt < NodeNum)
            cout << " ";
        if (last->left)
            que.push(last->left);
        if (last->right)
            que.push(last->right);
    }

    
}

int main()
{
    int NodeNum;
    cin >> NodeNum;

    for (int i = 0; i < NodeNum; i++)
        cin >> postOrder[i];
    for (int i = 0; i < NodeNum; i++)
        cin >> inOrder[i];

    Node* root;

    root = ConstructTree(0, NodeNum, 0, NodeNum);
    LevelOrderTraversal(root, NodeNum);
}