Sword finger offer - print binary tree from top to bottom - (queue structure)

Print binary tree from top to bottom

Print out each node of the binary tree from top to bottom , Nodes of the same layer are printed from left to right .

for example ：
Given binary tree : [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7

return ：

[3,9,20,15,7]

Tips ：

Total number of nodes <= 1000

solution

/** * Definition for a binary tree node. * struct TreeNode { * int val; * struct TreeNode *left; * struct TreeNode *right; * }; */


/** * Note: The returned array must be malloced, assume caller calls free(). */
struct queue{
    
    // 1.  Location of the current element 
    // 2.  The number of elements in the queue 
    int cur_elem_pos;
    int last_elem_pos;
    struct TreeNode *elem;
};

void init_queue(struct queue* q){
    
    q->cur_elem_pos = 0;
    q->last_elem_pos = 0;
    q->elem = (struct TreeNode *)malloc(sizeof(struct TreeNode)*1010);
}

//  Queue get queue head element 
struct TreeNode pop(struct queue *q){
    
    //  No judgment 
    struct TreeNode node = q->elem[q->cur_elem_pos];
    q->cur_elem_pos ++;
    return node;
}

void push(struct queue * q, struct TreeNode e){
    
    q->elem[q->last_elem_pos++] = e;
}

void printTree(struct queue *q, int *res, int *returnSize){
    
    if(q->cur_elem_pos == q->last_elem_pos){
    
        return;
    }
    //  Take elements from the queue 
    struct TreeNode node = pop(q);
    *returnSize += 1;
    *res = node.val;
    res++;
    if(node.left != NULL){
    
        push(q, *node.left);
    }
    if(node.right != NULL){
    
        push(q, *node.right);
    }
    printTree(q, res, returnSize);
}

int* levelOrder(struct TreeNode* root, int* returnSize){
    
    //  Initialize queue 
    struct queue *q = (struct queue*)malloc(sizeof(struct queue));
    init_queue(q);
    //  Assign a size of 1000, The type is int Space 
    int *res = malloc(sizeof(int)*1010);
    //  Initialize the length of the tree 
    *returnSize = 0;
    if(root == NULL){
    
        return res;
    }
    // push root to queue
    push(q, *root);
    // printTree
    printTree(q, res, returnSize);
    return res;
}