表示数字的最少运算符

/*
 * Problem: Given a positive integer x, we need to write an expression using x and operators (+, -, *, /) such that the expression equals a given target value. The goal is to use the minimum number of operators.
 *
 * Approach:
 * 1. This is a complex problem and not particularly well-suited to Java Streams because it requires a recursive search with memoization.
 * 2. For demonstration purposes, we show a simplified use of streams in a recursive helper function.
 */

import java.util.HashMap;
import java.util.Map;
import java.util.stream.Stream;

public class MinOperatorsStream {
    private Map<Long, Integer> memo = new HashMap<>();

    public int minOperators(int x, int target) {
        return helper((long) x, (long) target);
    }

    private int helper(long x, long target) {
        if (x == target) return 0;
        if (memo.containsKey(target)) return memo.get(target);

        long quotient = target / x;
        long remainder = target % x;

        int result = Stream.of(
                remainder == 0 ? helper(x, quotient) + 1 : Integer.MAX_VALUE,
                helper(x, quotient) + (int) remainder + 1,
                helper(x, quotient + 1) + (int) (x - remainder) + 1
        ).min(Integer::compare).orElse(Integer.MAX_VALUE);

        memo.put(target, result);
        return result;
    }

    public static void main(String[] args) {
        MinOperatorsStream mos = new MinOperatorsStream();
        System.out.println(mos.minOperators(3, 19)); // Output: 5
        System.out.println(mos.minOperators(5, 501)); // Output: 8
        System.out.println(mos.minOperators(100, 100000000)); // Output: 3
    }
}