102. 二叉树的层序遍历

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


/**
 * Return an array of arrays of size *returnSize.
 * The sizes of the arrays are returned as *returnColumnSizes array.
 * Note: Both returned array and *columnSizes array must be malloced, assume caller calls free().
 */
 #define MAXNODE 5000
 struct TreeNode  *treequeue[MAXNODE];
 
int** levelOrder(struct TreeNode* root, int* returnSize, int** returnColumnSizes){
    *returnSize=0;
    if(root==NULL){
        * returnSize=0;
        return NULL;
    }
    //二维数组分配内存
    int **ret=(int **)malloc(sizeof(int *)*MAXNODE);
    //不能够申请这么大空间，后面使用的时候按照需要申请，否则容易超时
    //for(int i=0;i<MAXNODE;i++){
    //    ret[i]=(int *)malloc(sizeof(int)*MAXNODE);
    //}
    //出参数分配内存
    *returnColumnSizes = (int *)malloc(sizeof(int) * MAXNODE);//注意这块也要分配内存

    int start=0;
    int end=0;
    
    treequeue[end++]=root;
    struct TreeNode  *tmptree=NULL;

    while(start<end){
        //当前层节点数
        (* returnColumnSizes)[*returnSize]=end-start;
        // 此处已经有长度可以在这里进行申请内存，减少时间使用
        ret[*returnSize] = (int *)malloc(sizeof(int) * (end-start));
        for(int i=0;i<(*returnColumnSizes)[*returnSize];i++){
            tmptree=treequeue[start];
            ret[*returnSize][i]=tmptree->val;
            if(tmptree->left){
                treequeue[end++]=tmptree->left;
            }
            if(tmptree->right){
                treequeue[end++]=tmptree->right;
            }
            start++;
        }
        (*returnSize)++;
    }
    return ret;
}