1127. ZigZagging on a Tree 解析

后序中序建树，然后标记层数。奇数层用个stack倒个序就好。

#include <iostream>#include <queue>#include <vector>#include <algorithm>#include <stack>#define MAX 35using namespace std;struct Node {int data;Node * Left; Node * Right;int level;Node() { Left = NULL; Right = NULL; };};typedef Node * Tree;int post[MAX];int in[MAX];int n;vector <int> ans;int FindIn(int inst, int ined ,int num) {for (int i = inst; i <= ined; i++) {if (in[i] == num)return i;}return -1;}Tree BuildTree(int inst,int ined,int postst,int posted) {Tree t = NULL;if ((inst <= ined) && (postst <= posted)) {t = new Node;t->data = post[posted];int pos = FindIn(inst, ined, post[posted]);if (pos == -1)return NULL;t->Left = BuildTree(inst, pos - 1, postst, postst + pos - inst -1);t->Right = BuildTree(pos + 1, ined, postst + pos - inst, posted - 1);}return t;}//Tree BuildTree(int inst, int ined, int postst, int posted) {//Tree t = new Node;////if (postst <= posted) {//t->data = post[posted];////int L = 0; int R = 0; int tempI = 0;//bool isFind = false, isLR = false;//for (int i = inst; i <= ined; i++) {//if (in[i] == post[posted]) {//isFind = true;//isLR = true;//tempI = i;//}////if (!isLR) L++;//else R++;//}//R--;// //if (isFind) {//t->Left = BuildTree(inst, tempI - 1, postst, postst + L - 1);//t->Right = BuildTree(tempI + 1, ined, postst + L, posted - 1);//}//else return NULL;//}//else t = NULL;////return t;////}void Level(Tree t) {queue <Node> q;stack <int> s;int pre;int level = 1;bool newlevel = false;if (t) {pre = t->data;t->level = 1;pre = 1;q.push(*t);while (!q.empty()) {Node temp = q.front();if (pre != temp.level) {pre = temp.level;newlevel = true;}if (newlevel) {while (!s.empty()) {ans.push_back(s.top());s.pop();}newlevel = false;}if (temp.level % 2 == 1) {s.push(temp.data);}else {ans.push_back(temp.data);}if (temp.Left) temp.Left->level = temp.level + 1, q.push(*temp.Left);if (temp.Right) temp.Right->level = temp.level + 1, q.push(*temp.Right);q.pop();}while (!s.empty()) {ans.push_back(s.top());s.pop();}}}int main() {cin >> n;for (int i = 1; i <= n; i++) {cin >> in[i];}for (int i = 1; i <= n; i++) {cin >> post[i];}Tree T = BuildTree(1,n,1,n);Level(T);for (int i = 0; i < ans.size()-1; i++) {cout << ans[i] << " ";}if (ans.size() > 1) {cout << ans[ans.size() - 1] << endl;}else if (ans.size() == 1) {cout << ans[0] << endl;}return 0;}