1140 Look-and-say Sequence （20 分）

Look-and-say sequence is a sequence of integers as the following:

D, D1, D111, D113, D11231, D112213111, ...

where D is in [0, 9] except 1. The (n+1)st number is a kind of description of the nth number. For example, the 2nd number means that there is one D in the 1st number, and hence it is D1; the 2nd number consists of one D (corresponding to D1) and one 1 (corresponding to 11), therefore the 3rd number is D111; or since the 4th number is D113, it consists of one D, two 1's, and one 3, so the next number must be D11231. This definition works for D = 1 as well. Now you are supposed to calculate the Nth number in a look-and-say sequence of a given digit D.

Input Specification:

Each input file contains one test case, which gives D (in [0, 9]) and a positive integer N (≤ 40), separated by a space.

Output Specification:

Print in a line the Nth number in a look-and-say sequence of D.

Sample Input:

1 8

Sample Output:

1123123111

作者: CHEN, Yue

单位: 浙江大学

时间限制: 400 ms

内存限制: 64 MB

代码长度限制: 16 KB

#include<iostream>
using namespace std;

int main(){
    string s;
    int n,j;
    cin >> s;
    cin >> n;
    while(--n){
        string ans;
        int cnt = 0;
        char pre = s[0];
        for(int i = 0; i < s.size(); i++){
            if(s[i] == pre) cnt++;
            else{
                ans += pre;
                ans += cnt + '0';
                pre = s[i];
                cnt = 1;
            }            
        }
        if(cnt > 0){
            ans += pre;
            ans += cnt +'0';
        }
        s = ans;        
    }
    cout << s;
    return 0;
}