归并排序TLE了怎么办20pts

#include <bits/stdc++.h>
#define MAXN 100001
using namespace std;
int n,a[MAXN],t[MAXN];

void merge_sort(int l,int r)
{
	if(l==r) return;
	int mid=(l+r)>>1;
	merge_sort(l,mid),merge_sort(mid+1,r);
	for (int i = l,j=l,k=mid+1; i <= r; i++)
	{	//j是左侧数组下标，k是右侧数组下标
		if (j==mid+1)//越界
		{
			t[i]=a[k++];
		}
		else if(k==r+1)
		{
			t[i]=a[j++];
		}
		else t[i]=a[j]<a[k]?a[j++]:a[k++];
	}
	for (int i = 1; i <= r; i++)//返回排序后结果供下次递归
	{
		a[i]=t[i];
	}
}

int main()
{
	scanf("%d",&n);
	for (int i = 1; i <= n; i++)
	{
		scanf("%d",&a[i]);
	}
	merge_sort(1,n);
	for (int i = 1; i <= n; i++)
	{
		printf("%d ",t[i]);
	}
}