由前序遍历和后序遍历构建二叉树的C语言代码

以下是由前序遍历和后序遍历构建二叉树的C语言代码：

#include <stdio.h>
#include <stdlib.h>

struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};

struct TreeNode* buildTreeHelper(int* preorder, int preStart, int preEnd, int* inorder, int inStart, int inEnd, int* postorder, int postStart, int postEnd) {
    if (preStart > preEnd || inStart > inEnd || postStart > postEnd) {
        return NULL;
    }

    struct TreeNode* root = (struct TreeNode*)malloc(sizeof(struct TreeNode));
    root->val = preorder[preStart];

    int inIndex = 0;
    for (int i = inStart; i <= inEnd; i++) {
        if (inorder[i] == root->val) {
            inIndex = i;
            break;
        }
    }

    int leftTreeSize = inIndex - inStart;
    int rightTreeSize = inEnd - inIndex;

    root->left = buildTreeHelper(preorder, preStart + 1, preStart + leftTreeSize, inorder, inStart, inIndex - 1, postorder, postStart, postStart + leftTreeSize - 1);
    root->right = buildTreeHelper(preorder, preStart + leftTreeSize + 1, preEnd, inorder, inIndex + 1, inEnd, postorder, postStart + leftTreeSize, postEnd - 1);

    return root;
}

struct TreeNode* buildTree(int* preorder, int preorderSize, int* inorder, int inorderSize, int* postorder, int postorderSize) {
    return buildTreeHelper(preorder, 0, preorderSize - 1, inorder, 0, inorderSize - 1, postorder, 0, postorderSize - 1);
}

void printTree(struct TreeNode* root) {
    if (root == NULL) {
        return;
    }
    printf("%d ", root->val);
    printTree(root->left);
    printTree(root->right);
}

int main() {
    int preorder[] = {1, 2, 4, 5, 3, 6, 7};
    int inorder[] = {4, 2, 5, 1, 6, 3, 7};
    int postorder[] = {4, 5, 2, 6, 7, 3, 1};

    int size = sizeof(preorder) / sizeof(preorder[0]);

    struct TreeNode* root = buildTree(preorder, size, inorder, size, postorder, size);

    printf("前序遍历结果：");
    printTree(root);
    printf("\n");

    return 0;
}

这里假设前序遍历为preorder，后序遍历为postorder，中序遍历为inorder。函数buildTreeHelper()用于构建二叉树，其中preStart和preEnd表示当前前序遍历序列的起始和结束位置，inStart和inEnd表示当前中序遍历序列的起始和结束位置，postStart和postEnd表示当前后序遍历序列的起始和结束位置。在函数中，首先根据前序遍历序列的第一个元素创建根节点root，然后在中序遍历序列中查找到root的位置inIndex，进而计算出左子树的大小leftTreeSize和右子树的大小rightTreeSize。接下来，分别递归构建左子树和右子树，并将根节点的左右子树指针指向左右子树的根节点。最后，返回根节点。函数buildTree()是对buildTreeHelper()的包装，传入前序遍历序列、中序遍历序列、后序遍历序列的起始位置和大小。函数printTree()用于前序遍历打印二叉树，方便验证结果。主函数中定义了三个遍历序列，通过buildTree()创建二叉树并打印前序遍历结果。