Luo Gu P2524 Uim Valentine's Day gift-that of Er (Hong expanding open)

Topic: P2524 Uim Valentine's Day gift of their · Er: https://www.luogu.org/problemnew/show/P2524

---

Title Description

Prequel: see Luo Gu P2525

Uim successfully sent them in the order of the hands of the N sister and maintain their harmony.

Uim now want to know, he chose the order that all of the N sister gift order, lexicographical first of several small.

Input and output formats

Input formats:

A first line integer N, the number of expressed N.

A second line integer X, represents a given arrangement.

Output formats:

An integer that represents the first of several small lexicographical order.

Sample input and output

Input Sample # 1:

3
231

Output Sample # 1:

4

Explanation

1<=N<=9

No spaces are arranged entered

---

 

Title very simple, very small range of data.

We can use next_permutation (&, & + n) to solve all cases of violence and judgment.

 

Here, the main explanation is open to expand health. (Information Baidu , blog )

Ah, very good. After reading the above information should be very clear.

Here is the note:

　　1. Be sure to find a number smaller than its current number to the right of (>).

　　2. Each number (n) multiplied! (Tot-n-1) wherein tot is the total number of the last must be decremented. (In this case, n 0 from beginning to end)

　　3. The final calculation result is - arranged lexicographically arranged smaller than the current, and arranged in order but also add a current.

 

AC Code:

 1 //
 2 #include <bits/stdc++.h>
 3 using namespace std;
 4 typedef long long ll;
 5 #define ri register ll
 6 
 7 ll n;
 8 string s;
 9 
10 ll jc(ll a)
11 {
12     ri ans=1;
13     for(ri i=1;i<=a;i++)
14     {
15         ans*=i;
16     }
17     return ans;
18 }
19 
20 ll cantor()
21 {
22     ri end=0;
23     for(ri i=0;i<=n-1;i++)
24     {
25         ri smaller=0;
26         for(ri j=i+1;j<=n-1;j++)
27         {
28             if(s[i]>s[j]) smaller++;
29         }
30         end+= smaller*jc(n-i-1);
31     }
32     return end+1;
33 }
34 
35 signed main()
36 {
37     ios::sync_with_stdio(0),cin.tie(0);
38     cin>>n;
39     cin>>s;
40     cout<<cantor();
41     return 0;
42 }
43 //