Description

Since Sonya is interested in robotics too, she decided to construct robots that will read and recognize numbers.

Sonya has drawn $\mathrm{nn\; numbers\; in\; a\; row,\; aiai\; is\; located\; in\; the\; ii\; -th\; position.\; She\; also\; has\; put\; a\; robot\; at\; each\; end\; of\; the\; row\; (to\; the\; left\; of\; the\; first\; number\; and\; to\; the\; right\; of\; the\; last\; number).\; Sonya\; will\; give\; a\; number\; to\; each\; robot\; (they\; can\; be\; either\; same\; or\; different)\; and\; run\; them.\; When\; a\; robot\; is\; running,\; it\; is\; moving\; toward\; to\; another\; robot,\; reading\; numbers\; in\; the\; row.\; When\; a\; robot\; is\; reading\; a\; number\; that\; is\; equal\; to\; the\; number\; that\; was\; given\; to\; that\; robot,\; it\; will\; turn\; off\; and\; stay\; in\; the\; same\; position.}$

Sonya does not want robots to break, so she will give such numbers that robots will stop before they meet. That is, the girl wants them to stop at different positions so that the first robot is to the left of the second one.

For example, if the numbers $[1,5,4,1,3][1,5,4,1,3]\; are\; written,\; and\; Sonya\; gives\; the\; number$

Sonya understands that it does not make sense to give a number that is not written in the row because a robot will not find this number and will meet the other robot.

Sonya is now interested in finding the number of different pairs that she can give to robots so that they will not meet. In other words, she wants to know the number of pairs ($\mathrm{pp\; ,\; qq\; ),\; where\; she\; will\; give\; pp\; to\; the\; first\; robot\; and\; qq\; to\; the\; second\; one.\; Pairs\; (pipi\; ,\; qiqi\; )\; and\; (pjpj\; ,\; qjqj\; )\; are\; different\; if\; pi\ne pjpi\ne pj\; or\; qi\ne qjqi\ne qj\; .}$

Unfortunately, Sonya is busy fixing robots that broke after a failed launch. That is why she is asking you to find the number of pairs that she can give to robots so that they will not meet.

Input

The first line contains a single integer $\mathrm{nn\; (1\le n\le 1051\le n\le 105\; )\; —\; the\; number\; of\; numbers\; in\; a\; row.}$

The second line contains $\mathrm{nn\; integers\; a1,a2,\dots ,ana1,a2,\dots ,an\; (1\le ai\le 1051\le ai\le 105\; )\; —\; the\; numbers\; in\; a\; row.}$

Output

Print one number — the number of possible pairs that Sonya can give to robots so that they will not meet.

Sample Input

5
1 5 4 1 3

9

7
1 2 1 1 1 3 2

7

Sample Output

Hint

In the first example, Sonya can give pairs ($\mathrm{11\; ,\; 11\; ),\; (11\; ,\; 33\; ),\; (11\; ,\; 44\; ),\; (11\; ,\; 55\; ),\; (44\; ,\; 11\; ),\; (44\; ,\; 33\; ),\; (55\; ,\; 11\; ),\; (55\; ,\; 33\; ),\; and\; (55\; ,\; 44\; ).}$

In the second example, Sonya can give pairs ($\mathrm{11\; ,\; 11\; ),\; (11\; ,\; 22\; ),\; (11\; ,\; 33\; ),\; (22\; ,\; 11\; ),\; (22\; ,\; 22\; ),\; (22\; ,\; 33\; ),\; and\; (33\; ,\; 22\; ).}$

$\mathrm{題目大意:有n個數,每個數只能與自己後面的數配對,相同的配對只算一個,求配對的數量.}$

$\mathrm{分析：我們可以倒著往前壓，把數放進map(去重操作）中，從後往前放入容器中，ans[i]就等於容器中元素的個數，並且我們用mp[str[i]]=i,記錄該元素第一次出現的位置以方便後面的更新，若該元素第二次出現，上一次出現的位置ans[pos]=0,因為位置越靠前，配對的個數越多}$

 1 #include <iostream>
 2 #include<cmath>
 3 #include<cstdio>
 4 #include<cstring>
 5 #include<stack>
 6 #include<queue>
 7 #include<deque>
 8 #include<map>
 9 #include<algorithm>
10 #define PI acos(-1.0)
11 using namespace std;
12 typedef long long ll;
13 map<int,int>::iterator it;
14 int str[111234];
15 int ans[123114];
16 int m,n;
17 int main()
18 {
19     scanf("%d",&m);
20     map<int,int>mp;
21     mp.clear();
22     for(int i=1;i<=m;i++)
23     {
24         scanf("%d",&str[i]);
25     }
26     for(int i=m;i>=1;i--)
27     {
28         ans[i]=mp.size();
29         if(mp.count(str[i]))//更新操作，若該元素第二次出現，上一次的ans賦值為0
30         {
31             ans[mp[str[i]]]=0;
32         }
33         mp[str[i]]=i;
34     }
35     ans[m+1]=‘\0‘;
36     ll sum=0;
37      for(int i=1;i<=m;i++)
38         sum+=ans[i];
39         printf("%lld\n",sum);
40      return 0;
41 
42 }

Codeforces Round #495 (Div. 2)(1004C)