Uva--122 Trees on the level(二叉树的层次遍历)

记录
23:27 2023-4-20

https://onlinejudge.org/external/1/122.pdf

reference:《算法竞赛入门经典第二版》例题6-7

二叉树的层次遍历，这里是直接复制了作者的代码。(之前在我的数据结构学习里面手写过树、二叉树、AVL树(说是手写，其实也是照着浙大那个数据结构公开课，参考书是Data Structures and Algorithm Analysis in C/C++/JAVA)，前序中序后序也都实现过) 遗憾的是，书上有些内容课程是没有讲到的(毕竟是主要讲数据结构)，后面我也没把它看完，刚粗略看了下，没看过的有第九章图论算法的网络流和深度优先搜索的应用、第十章算法设计技巧、第十一章摊还分析、第十二章高级数据结构及其实现(红黑树在这，所以我没看:( )，这些内容还是有必要看滴，之后有时间?应该会看，嘎！

// UVa122 Trees on the level
// Rujia Liu
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<vector>
#include<queue>
using namespace std;

const int maxn = 256 + 10;

struct Node{
  bool have_value;
  int v;
  Node* left, *right;
  Node():have_value(false),left(NULL),right(NULL){}
};

Node* root;

Node* newnode() { return new Node(); }

bool failed;
void addnode(int v, char* s) {
  int n = strlen(s);
  Node* u = root;
  for(int i = 0; i < n; i++)
    if(s[i] == 'L') {
      if(u->left == NULL) u->left = newnode();
      u = u->left;
    } else if(s[i] == 'R') {
      if(u->right == NULL) u->right = newnode();
      u = u->right;
    }
  if(u->have_value) failed = true;
  u->v = v;
  u->have_value = true;
}

void remove_tree(Node* u) {
  if(u == NULL) return;
  remove_tree(u->left);
  remove_tree(u->right);
  delete u;
}

char s[maxn];
bool read_input() {
  failed = false;
  remove_tree(root);
  root = newnode();
  for(;;) {
    if(scanf("%s", s) != 1) return false;
    if(!strcmp(s, "()")) break;
    int v;
    sscanf(&s[1], "%d", &v);
    addnode(v, strchr(s, ',')+1);
  }
  return true;
}

bool bfs(vector<int>& ans) {
  queue<Node*> q;
  ans.clear();
  q.push(root);
  while(!q.empty()) {
    Node* u = q.front(); q.pop();
    if(!u->have_value) return false;
    ans.push_back(u->v);
    if(u->left != NULL) q.push(u->left);
    if(u->right != NULL) q.push(u->right);
  }
  return true;
}

int main() {
  vector<int> ans;
  while(read_input()) {
    if(!bfs(ans)) failed = 1;
    if(failed) printf("not complete\n");
    else {
      for(int i = 0; i < ans.size(); i++) {
        if(i != 0) printf(" ");
        printf("%d", ans[i]);
      }
      printf("\n");
    }
  }
  return 0;
}