Dfs类型题
收获：明确二叉树的三种优先遍历，以及用c++输入流输出流的使用
1 #include<cstdio> 2 #include<cmath> 3 #include<algorithm> 4 #include<cstring> 5 #include<cstdlib> 6 #include<sstream> 7 #include<iostream> 8 9 using namespace std; 10 const int MaxN = 1e4; 11 int in_order[MaxN + 5], post_order[MaxN + 5]; 12 int lch[MaxN+ 5], rch[MaxN + 5]; 13 int n; 14 int best, best_sum = 1<<30; 15 16 bool read_list(int *a) 17 { 18 string line; 19 if(!getline(cin, line)) return false; 20 stringstream ss(line); 21 n = 0; 22 int x; 23 while(ss >> x) a[n++] = x; 24 return n > 0; 25 } 26 27 int Build(int L1, int R1, int L2, int R2) 28 { 29 if(L1 > R1)return 0; 30 int root = post_order[R2]; 31 int p = L1; 32 while(in_order[p] != root) p++; 33 int cnt = p - L1; 34 lch[root] = Build(L1, p - 1, L2, L2 + cnt - 1); 35 rch[root] = Build(p + 1, R1, L2 + cnt, R2 - 1); 36 return root; 37 } 38 void Dfs(int u, int sum) 39 { 40 sum = sum + u; 41 if(!lch[u] && !rch[u]) 42 { 43 if(sum < best_sum || (sum == best_sum && u < best)) 44 { 45 best = u; 46 best_sum = sum; 47 } 48 } 49 if(lch[u]) Dfs(lch[u], sum); 50 if(rch[u]) Dfs(rch[u], sum); 51 } 52 53 int main() 54 { 55 while(read_list(in_order)) 56 { 57 best_sum = 1<<30; 58 read_list(post_order); 59 Build(0, n - 1, 0, n - 1); 60 Dfs(post_order[n - 1], 0); 61 cout << best << " "; 62 } 63 return 0; 64 } 65