LeetCode-in-Java

1237. Find Positive Integer Solution for a Given Equation

Medium

Given a callable function f(x, y) with a hidden formula and a value z, reverse engineer the formula and return all positive integer pairs x and y where f(x,y) == z. You may return the pairs in any order.

While the exact formula is hidden, the function is monotonically increasing, i.e.:

• f(x, y) < f(x + 1, y)
• f(x, y) < f(x, y + 1)

The function interface is defined like this:

interface CustomFunction { public: // Returns some positive integer f(x, y) for two positive integers x and y based on a formula. int f(int x, int y); };

We will judge your solution as follows:

• The judge has a list of 9 hidden implementations of CustomFunction, along with a way to generate an answer key of all valid pairs for a specific z.
• The judge will receive two inputs: a function_id (to determine which implementation to test your code with), and the target z.
• The judge will call your findSolution and compare your results with the answer key.
• If your results match the answer key, your solution will be `

Solution

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class Solution {
    // This is the custom function interface.
    // You should not implement it, or speculate about its implementation
    public interface CustomFunction {
        // Returns f(x, y) for any given positive integers x and y.
        // Note that f(x, y) is increasing with respect to both x and y.
        // i.e. f(x, y) < f(x + 1, y), f(x, y) < f(x, y + 1)
        int f(int x, int y);
    }

    public List<List<Integer>> findSolution(CustomFunction customfunction, int z) {
        List<List<Integer>> result = new ArrayList<>();
        int x = 1;
        int y = 1000;
        while (x < 1001 && y > 0) {
            int functionResult = customfunction.f(x, y);
            if (functionResult < z) {
                x++;
            } else if (functionResult > z) {
                y--;
            } else {
                result.add(Arrays.asList(x++, y--));
            }
        }
        return result;
    }
}

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