PAT A1140 Look-and-say Sequence (20point(s))

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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

解答

#include<iostream>
#include<string>

using namespace std;

int main(){
	string str; 
	int n, j = 0;
	cin >> str >> n;
	for (int k = 1; k < n; k++) {
		string tmp;
		for (int i = 0; i < str.length(); i = j) {
			for (j = i; j < str.length() && str[j] == str[i]; j++);
			tmp += str[i] + to_string(j - i);
		}
		str = tmp;
	}
	cout << str;
	return 0;
}