二叉树的三种遍历方式

 1 #include<stdio.h>
 2 #include<iostream>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<string>
 6 #include<sstream>
 7 using namespace std;
 8 
 9 const int INF = 0x3f3f3f3f;
10 //因为各节点的权值各不相同且都只是整数，直接用权值作为节点编号
11 const int maxn = 10000 + 10;    
12 int in_order[maxn], post_order[maxn], lch[maxn], rch[maxn];
13 int n;
14 int best, best_sum;
15 
16 //按行读取数据，并存到数组中
17 bool read_list(int *a)
18 {
19     string line;
20     if (!getline(cin, line))  return false;
21     stringstream ss(line);
22     n = 0;
23     int x;
24     while (ss >> x)  a[n++] = x;
25     return n > 0;
26 }
27 
28 //把in_order[L1,R1]和post_order[L2,R2]建成一棵二叉树，返回树根
29 int build(int L1, int R1, int L2, int R2)
30 {
31     if (L2 > R2)  return 0;  //空树
32     int root = post_order[R2];
33     int pos = L1;
34     while (in_order[pos] != root)  pos++;
35     int cnt = pos - L1;
36     lch[root] = build(L1, pos - 1, L2, L2 + cnt - 1);
37     rch[root] = build(pos + 1, R1, L2 + cnt, R2 - 1);
38     return root;
39 }
40 
41 //从根节点出发，中序遍历，查找最小值
42 void dfs(int u, int sum)
43 {
44     sum += u;
45 
46     //到达叶子节点，循环终止
47     if (!lch[u] && !rch[u])
48     {
49         if (sum < best_sum)
50         {
51             best = u;
52             best_sum = sum;
53         }
54         return;
55     }
56 
57     //加了个剪枝：如果当前的和大于当前的最小和，就不必从这条路继续搜
58     if (lch[u] && sum < best_sum)  dfs(lch[u], sum);
59     if (rch[u] && sum < best_sum)  dfs(rch[u], sum);
60 }
61 
62 int main()
63 {
64     while (read_list(in_order))
65     {
66         read_list(post_order);
67         build(0, n - 1, 0, n - 1);
68 
69         best_sum = INF;
70         dfs(post_order[n - 1], 0);
71         cout << best << endl;
72     }
73     return 0;
74 }