重构二叉树
根据后序中序重构二叉树，并输出层次遍历模板
1 /**\ 2 input: 3 7 4 2 3 1 5 7 6 4 5 1 2 3 4 5 6 7 6 7 output: 8 4 1 6 3 5 7 2 9 \**/ 10 #include <bits/stdc++.h> 11 12 using namespace std; 13 14 const int N = 40; 15 16 int a[N], b[N];//后序 中序 17 18 int n; 19 unordered_map<int, int > L, R; // L[i]表示i的左儿子 R[i]表示i的右儿子 20 21 //后序遍历区间[la,ra] 中序遍历区间[lb, rb] 22 int build(int la, int ra, int lb, int rb) 23 { 24 if(la > ra) return 0; //越界返回 25 int root = a[ra]; //根节点 26 int i; 27 for(i = lb; i <= rb && b[i] != root; i++) {} 28 if(i <= rb) 29 { 30 L[root] = build(la, ra - rb + i - 1, lb, i - 1); 31 R[root] = build(ra - rb + i, ra - 1, i + 1, rb); 32 } 33 return root; 34 } 35 void bfs(int root) 36 { 37 queue<int> q; 38 q.push(root); 39 int f = 0; 40 while(!q.empty()) 41 { 42 int now = q.front(); 43 q.pop(); 44 f == 0 ? printf("%d", now) : printf(" %d", now); 45 f++; 46 if(L[now]) q.push(L[now]); 47 if(R[now]) q.push(R[now]); 48 } 49 } 50 51 52 signed main() 53 { 54 scanf("%d", &n); 55 for(int i = 1; i <= n; ++i) scanf("%d", &a[i]); 56 for(int i = 1; i <= n; ++i) scanf("%d", &b[i]); 57 int root = build(1, n, 1, n); 58 bfs(root); 59 return 0; 60 }
