題意：

給定一顆樹， 按層次遍歷輸出。

分析：

用數組模擬二叉樹， bfs即可實現層次遍歷

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 struct Node{
 4     bool have_value;
 5     int v, left, right;
 6     void reset(){//用於再次初始化節點
 7         init();
 8     }
 9     void init(){
10         have_value = 0;
11         v = left = right = 0
 
;
12     }
13     Node():have_value(false), v(0),left(0), right(0){init();}//構造函數
14 };
15 const int maxn = 512;
16 Node tree[maxn];
17 const int root = 1;
18 int cnt, failed;
19 char s[maxn];
20 void newtree(){
21     cnt = 1;
22     tree[root].reset();
23 }
24 void addnode(int v, char* s){
25 
26     int
 
 len = strlen(s) - 1;
27     int u = root;
28     for(int i = 0; i < len; i++){
29         if(s[i] == ‘L‘){
30             if(tree[u].left == 0)
31             {
32                 tree[u].left = ++cnt;
33                 tree[cnt].reset();
34                 u = cnt;
35             }
36             else
 
 { u = tree[u].left;};
37         }
38         else if(s[i] == ‘R‘){
39             if(tree[u].right == 0){
40                 tree[u].right = ++cnt;
41                 tree[cnt].reset();
42                 u = cnt;
43             }
44             else u = tree[u].right;
45         }
46     }
47     if(tree[u].have_value) failed = true;
48     tree[u].v = v;
49     tree[u].have_value = true;
50 }
51 bool input(){
52     newtree();
53     failed = false;
54     for(;;){
55         if(scanf("%s",s) != 1) return false;
56         if(!strcmp(s,"()")) break;
57         int v;
58         sscanf(&s[1],"%d",&v);
59         addnode(v,strchr(s,‘,‘)+1);//將逗號後的字符串傳遞
60     }
61     return true;
62 }
63 bool bfs(vector<int>& ans){//引用傳遞
64     queue<int> q;
65     q.push(root);
66     while(!q.empty()){
67         int u = q.front();
68         q.pop();
69         if(tree[u].have_value == 0)
70             return false;
71         ans.push_back(tree[u].v);
72         if(tree[u].left != 0){
73             q.push(tree[u].left);
74         }
75         if(tree[u].right != 0){
76             q.push(tree[u].right);
77         }
78     }
79     return true;
80 }
81 int main(){
82 
83     while(input()){
84         vector<int> ans;
85         if(!bfs(ans) || failed)
86             printf("not complete\n");
87         else {
88             cout <<ans[0];
89             int alen = ans.size();
90             for(int i = 1; i < alen; i++){
91                 cout << " " << ans[i];
92             }
93             puts("");
94         }
95     }
96     return 0;
97 }

UVa 122 樹的層次遍歷