Find Permutation

Given a positive integer n and a string s consisting only of letters D or I, you have to find any permutation of first n positive integer that satisfy the given input string.

D means the next number is smaller, while I means the next number is greater.

Notes

• Length of given string s will always equal to n - 1

• Your solution should run in linear time and space.

Example :

Input 1:

n = 3

s = ID

Return: [1, 3, 2]

public class Solution {
    public ArrayList<Integer> findPerm(String A, int B) {
        int end = B, start = 1;
        ArrayList<Integer> ans = new ArrayList<>();
        for (int i = 0; i < A.length(); i++) {
            if (A.charAt(i) == 'I')
                ans.add(start++);
            else
                ans.add(end--);
        }
        if (A.charAt(A.length() - 1) == 'D')
            ans.add(start);
        else
            ans.add(end);
        return ans;
    }
}