普通老方法：

#include <bits/stdc++.h>
#define INF 0x3f3f3f3f
#define PI acos(-1.0)
#define N 100001
#define MOD 123
#define E 1e-6
using namespace std;
char a[N],b[N],c[N];
int calculate(int left1,int right1,int left2,int right2)
{
    if(left1==right1)
    {
        c[left1]=1;
        return c[left1];
    }
    int i;
    for(i=left2;i<=right2;i++)
        if(a[left1]==b[i])
            break;
    if(left2<i)
        c[left1]+=calculate(left1+1,(i-1-left2)+(left1+1),left2,i-1);
    if(i<right2)
        c[left1]+=calculate(right1-(right2-(i+1)),right1,i+1,right2);
    return c[left1];
}
int main()
{
    cin>>a>>b;
    int lena=strlen(a);
    int lenb=strlen(b);
    calculate(0,lena-1,0,lenb-1);
    for(int i=0;i<lena;i++)
    {
        for(int j=1;j<=c[i];j++)
            cout<<a[i];
        cout<<endl;
    }
    return 0;
}

结构体非指针方式：

#include <bits/stdc++.h>
using namespace std;
static const int MAXN = 100; // 假定最多100个节点
struct Node {
    char c;    // 节点字符
    int left;  // 左子节点索引
    int right; // 右子节点索引
};
string preOrder, inOrder;
Node tree[MAXN];
int nodeCount;
int charToIndex[256]; // 通过字符快速找到其在 tree 中的下标
// 根据 preOrder[preL...preR] 和 inOrder[inL...inR] 重建树，返回根节点索引
int buildTree(int preL, int preR, int inL, int inR) {
    if (preL > preR || inL > inR) return -1;

    char rootChar = preOrder[preL];
    // 找到rootChar在中序中的位置
    int rootPos = inL;
    while (rootPos <= inR && inOrder[rootPos] != rootChar) {
        rootPos++;
    }

    // 创建根节点
    int rootIndex = charToIndex[(unsigned char)rootChar];

    int leftSize = rootPos - inL; // 左子树节点数
    // 递归构建左子树
    tree[rootIndex].left = buildTree(preL + 1, preL + leftSize, inL, rootPos - 1);
    // 递归构建右子树
    tree[rootIndex].right = buildTree(preL + leftSize + 1, preR, rootPos + 1, inR);

    return rootIndex;
}

// 计算节点长度（叶子为1，非叶为左右子树长度和）
int calcLength(int root) {
    if (root == -1) return 0;
    int leftLen = calcLength(tree[root].left);
    int rightLen = calcLength(tree[root].right);
    if (leftLen == 0 && rightLen == 0) {
        return 1; // 叶子节点长度为1
    }
    return leftLen + rightLen;
}

// 凹入表示法输出
void printTree(int root) {
    if (root == -1) return;
    int leftLen = (tree[root].left == -1 ? 0 : calcLength(tree[root].left));
    int rightLen = (tree[root].right == -1 ? 0 : calcLength(tree[root].right));
    int length = (leftLen == 0 && rightLen == 0) ? 1 : leftLen + rightLen;

    for (int i = 0; i < length; i++) {
        cout << tree[root].c;
    }
    cout << "\n";

    // 输出左子树
    printTree(tree[root].left);
    // 输出右子树
    printTree(tree[root].right);
}

int main() {
    // 读入先序和中序遍历
    cin >> preOrder >> inOrder;
    // 假设节点数为 preOrder.length() 或 inOrder.length()
    nodeCount = (int)preOrder.size();

    // 初始化map
    for (int i = 0; i < 256; i++) {
        charToIndex[i] = -1;
    }

    // 根据 preOrder 字符创建节点数组，并记录字符到下标的映射
    for (int i = 0; i < nodeCount; i++) {
        tree[i].c = preOrder[i];
        tree[i].left = -1;
        tree[i].right = -1;
        charToIndex[(unsigned char)preOrder[i]] = i;
    }

    // 建树
    int root = buildTree(0, nodeCount - 1, 0, nodeCount - 1);

    // 输出
    printTree(root);

    return 0;
}