用C写一个二叉树求先序遍历中序遍历后序遍历层次遍历

下面是使用C语言实现二叉树的先序遍历、中序遍历、后序遍历和层次遍历的代码。

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

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

// 创建新节点
TreeNode* createNode(int val) {
    TreeNode* node = (TreeNode*)malloc(sizeof(TreeNode));
    node->val = val;
    node->left = NULL;
    node->right = NULL;
    return node;
}

// 先序遍历
void preOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    printf("%d ", root->val); // 输出节点值
    preOrder(root->left);
    preOrder(root->right);
}

// 中序遍历
void inOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    inOrder(root->left);
    printf("%d ", root->val); // 输出节点值
    inOrder(root->right);
}

// 后序遍历
void postOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    postOrder(root->left);
    postOrder(root->right);
    printf("%d ", root->val); // 输出节点值
}

// 层次遍历
void levelOrder(TreeNode* root) {
    if (root == NULL) {
        return;
    }
    TreeNode* queue[1000];
    int front = 0, rear = 0;
    queue[rear++] = root;
    while (front != rear) {
        TreeNode* cur = queue[front++];
        printf("%d ", cur->val); // 输出节点值
        if (cur->left != NULL) {
            queue[rear++] = cur->left;
        }
        if (cur->right != NULL) {
            queue[rear++] = cur->right;
        }
    }
}

int main() {
    // 创建二叉树
    TreeNode* root = createNode(1);
    root->left = createNode(2);
    root->right = createNode(3);
    root->left->left = createNode(4);
    root->left->right = createNode(5);
    root->right->left = createNode(6);
    root->right->right = createNode(7);

    printf("先序遍历: ");
    preOrder(root);
    printf("\n");

    printf("中序遍历: ");
    inOrder(root);
    printf("\n");

    printf("后序遍历: ");
    postOrder(root);
    printf("\n");

    printf("层次遍历: ");
    levelOrder(root);
    printf("\n");

    return 0;
}

输出结果为：

先序遍历: 1 2 4 5 3 6 7 
中序遍历: 4 2 5 1 6 3 7 
后序遍历: 4 5 2 6 7 3 1 
层次遍历: 1 2 3 4 5 6 7