二叉树的建立

#include <bits/stdc++.h>
using namespace std;
int a[105],t=0;
struct TreeNode {
    int val;
    struct TreeNode *left;
    struct TreeNode *right;
};
TreeNode* build(TreeNode * &root,int g)
{
    if(g>t||a[g]==0)
    {
        root=NULL;
        return root;
    }
    root=(TreeNode*)malloc(sizeof(TreeNode));
    root->val=a[g];
    build(root->left,2*g);
    build(root->right,2*g+1);
    return root;
}
int main()
{
    int n,m,i,j,k;
    while(cin>>k,k!=-1)
    a[++t]=k;
    TreeNode *root;
    root=build(root,1);
    cout<<k<<endl;
}