c语言层次遍历二叉树完整代码

C语言层次遍历二叉树的完整代码如下：

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

// 树节点的结构体
typedef struct TreeNode {
    int val;
    struct TreeNode* left;
    struct TreeNode* right;
} TreeNode;

// 定义队列结构体
typedef struct QueueNode {
    struct TreeNode* data;
    struct QueueNode* next;
} QueueNode;

// 定义队列
typedef struct Queue {
    QueueNode* front;
    QueueNode* rear;
} Queue;

// 初始化队列
void initQueue(Queue* q) {
    q->front = q->rear = NULL;
}

// 判断队列是否为空
int isEmpty(Queue* q) {
    return q->front == NULL;
}

// 入队
void enqueue(Queue* q, TreeNode* node) {
    QueueNode* newNode = (QueueNode*)malloc(sizeof(QueueNode));
    newNode->data = node;
    newNode->next = NULL;

    if (isEmpty(q)) {
        q->front = q->rear = newNode;
    } else {
        q->rear->next = newNode;
        q->rear = newNode;
    }
}

// 出队
TreeNode* dequeue(Queue* q) {
    if (isEmpty(q)) {
        return NULL;
    }

    QueueNode* node = q->front;
    TreeNode* data = node->data;

    if (q->front == q->rear) {
        q->front = q->rear = NULL;
    } else {
        q->front = q->front->next;
    }

    free(node);

    return data;
}

// 层次遍历二叉树
void levelOrderTraversal(TreeNode* root) {
    if (root == NULL) {
        return;
    }

    Queue q;
    initQueue(&q);
    enqueue(&q, root);

    while (!isEmpty(&q)) {
        TreeNode* node = dequeue(&q);
        printf("%d ", node->val);

        if (node->left) {
            enqueue(&q, node->left);
        }

        if (node->right) {
            enqueue(&q, node->right);
        }
    }
}

int main() {
    // 构造二叉树
    TreeNode* root = (TreeNode*)malloc(sizeof(TreeNode));
    root->val = 1;

    TreeNode* left = (TreeNode*)malloc(sizeof(TreeNode));
    left->val = 2;

    TreeNode* right = (TreeNode*)malloc(sizeof(TreeNode));
    right->val = 3;

    TreeNode* leftLeft = (TreeNode*)malloc(sizeof(TreeNode));
    leftLeft->val = 4;

    TreeNode* leftRight = (TreeNode*)malloc(sizeof(TreeNode));
    leftRight->val = 5;

    root->left = left;
    root->right = right;

    left->left = leftLeft;
    left->right = leftRight;

    right->left = right->right = leftLeft->left = leftLeft->right = leftRight->left = leftRight->right = NULL;

    // 层次遍历二叉树
    levelOrderTraversal(root);

    return 0;
}

在代码中，我们使用了队列来实现层次遍历。具体思路是先将根节点入队，然后依次出队，访问其左右子节点，再将左右子节点入队，以此类推，直到队列为空。