根据模式串构造最小数字

/*
 * Problem Description:
 * Given a pattern string containing 'I' (increase) and 'D' (decrease),
 * construct the smallest lexicographical permutation of numbers '1' to '9'
 * such that for every 'I' in the pattern, the corresponding numbers in the result
 * are increasing, and for every 'D', they are decreasing.
 * 
 * Approach (using Java Streams):
 * 1. Create a list of integers from 1 to 9.
 * 2. Use a Deque to manage the sequence according to 'I' and 'D' pattern.
 * 3. Iterate through the pattern and modify the Deque accordingly.
 * 4. Convert the Deque to a string and return the result.
 */

import java.util.*;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class SolutionStream {
    public String smallestNumber(String pattern) {
        List<Integer> numbers = IntStream.rangeClosed(1, 9).boxed().collect(Collectors.toList());
        Deque<Integer> deque = new LinkedList<>();
        for (int i = 0; i <= pattern.length(); i++) {
            deque.offerLast(numbers.get(i));
            if (i == pattern.length() || pattern.charAt(i) == 'I') {
                while (!deque.isEmpty()) {
                    deque.pollFirst();
                }
            }
        }
        return deque.stream().map(String::valueOf).collect(Collectors.joining());
    }
}