poj2255Tree Recovery【二叉树重构】

大意：告诉你一棵二叉树的先序遍历和中序遍历求该二叉树的后续遍历

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;

const int maxn = 30;
char pr[maxn], mi[maxn];

struct Node {
    int left;
    int right;
}tr[maxn];

int root;

void init(int p) {
    tr[p].left = -1;
    tr[p].right = -1;
}

void fason(int pa, int son) {
    if(son < pa) {
        if(tr[pa].left == -1) {
            init(son);
            tr[pa].left = son;
        } else fason(tr[pa].left, son);
    } else {
        if(tr[pa].right == -1) {
            init(son);
            tr[pa].right = son;
        } else fason(tr[pa].right, son);
    }
}

void build_tree() {
    for(int i = 0; mi[i]; i++) {
        if(mi[i] == pr[0]) {
            root = i;
            init(root);
            break;
        }
    }
    for(int i =1; pr[i]; i++) {
        for(int j = 0; mi[j]; j++) {
            if(mi[j] == pr[i]) {
                fason(root, j);
                break;
            }
        }
    }
}
void pre_out(int p) {
    printf("%c", mi[p]);
    if(tr[p].left != -1) pre_out(tr[p].left);
    if(tr[p].right != -1) pre_out(tr[p].right);
}
void mid_out(int p) {
    if(tr[p].left != -1) mid_out(tr[p].left);
    printf("%c", mi[p]);
    if(tr[p].right != -1) mid_out(tr[p].right);
}

void back_out(int p) {
    if(tr[p].left != -1) back_out(tr[p].left);
    if(tr[p].right != -1) back_out(tr[p].right);
    printf("%c", mi[p]);
}

int main() {
    while(EOF != scanf("%s %s",pr, mi) ) {
        build_tree();
        pre_out(root);
        puts("");
        mid_out(root);
        puts("");
        back_out(root);
        puts("");
    }
    return 0;
}