STL unordered_map模数冲突

CodeForces 977F. Consecutive Subsequence

unordered_map用Hashtable实现，操作均摊常数时间复杂度，但是可能存在模数冲突，会被卡到On导致TLE，最好手写一个hash映射，防止被卡。当然，时间允许的话可以用map的稳定logn时间复杂度。

AC代码：

struct node
{
    int siz,idx;
};
inline int gethash(int x)//手写映射
{
    return x*1331+1333331;
}
unordered_map<int, node> mp; // num size idx
int ans[200010], ct;
int a[200010];
int main()
{
    int n;
    scanf("%d", &n);
    for (int i = 1; i <= n; i++)
    {
        scanf("%d",&a[i]);
        mp[gethash(a[i])].siz = mp[gethash(a[i]-1)].siz + 1;
        mp[gethash(a[i])].idx = i;
    }
    int pos, maxx = -1,pos2;
    for (unordered_map<int, node>::iterator it = mp.begin(); it != mp.end(); it++)
        if (it->second.siz > maxx)
        {
            maxx = it->second.siz;
            pos2=it->second.idx;
        }
    pos =a[pos2]-maxx+1;
    printf("%d\n",maxx);
    for(int i =1; i<=n; i++)
        if(a[i]==pos)
        {
            printf("%d ",i);
            pos++;
        }
    return 0;
}