AgoDeep.java

import java.security.InvalidParameterException;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class AlgoDeep {
    Integer maxHeight;
    Integer maxHeightIndex;
    Integer maxNextHeight;
    Integer maxNextHeightIndex;

    int lowerElement = Integer.MAX_VALUE;
    int maxDeep = 0;

    private void calc(int[] input) {
        if (input.length < 3) {
            throw new InvalidParameterException("There must be more than 2 elements in array!");
        }
        for (int i = 0; i < input.length; i++) {
            setVariables(input, i);

            if (maxNextHeight != null && maxHeight < maxNextHeight && i > 0) {
                if (i > 1)
                    setMaxDeep(input, i);
                startOver(input, i);
            }

            if (maxNextHeight != null && maxHeight > maxNextHeight && i > 0) {
                lowerElement = (input[i] > lowerElement && lowerElement != Integer.MAX_VALUE) ? lowerElement : input[i];
            }

            if (i == input.length - 1) {
                setMaxDeep(input, i);
            }
        }
    }

    private void startOver(int[] input, int i) {
        maxHeight = input[i];
        maxHeightIndex = i;
        maxNextHeight = null;
        maxNextHeightIndex = null;
        lowerElement = Integer.MAX_VALUE;
    }

    public static void main(String[] args) {
        int[] input = {2, 4, 3, 3, 5, 1, 2, 1, 2, 3, 1};

        AlgoDeep algoDeep = new AlgoDeep();
        algoDeep.calc(input);

        System.out.println(Arrays.toString(input));
        System.out.println(algoDeep.maxDeep);
        assert algoDeep.maxDeep == 2;

        AlgoDeep algoDeep2 = new AlgoDeep();
        int[] input2 = {1, 3, 2, 1, 2, 1, 5, 3, 3, 4, 2};
        algoDeep2.calc(input2);
        System.out.println(Arrays.toString(input2));
        System.out.println(algoDeep2.maxDeep);
        assert algoDeep2.maxDeep == 2;

        AlgoDeep algoDeep3 = new AlgoDeep();
        int[] input1 = {3, 1, 3, 2, 1, 2, 1, 5, 3, 3, 4, 2};
        algoDeep3.calc(input1);
        System.out.println(Arrays.toString(input1));
        System.out.println(algoDeep3.maxDeep);
        assert algoDeep3.maxDeep == 2;
        
        AlgoDeep algoDeep4 = new AlgoDeep();
        int[] input3 = {3, 5, 2, 4};
        algoDeep4.calc(input3);
        System.out.println(Arrays.toString(input3));
        System.out.println(algoDeep4.maxDeep);
        assert algoDeep4.maxDeep == 2;
    }

    private void setVariables(int[] input, int i) {
        if (maxHeight != null && i != 0) {
            maxNextHeight = input[i];
            maxNextHeightIndex = i;
        }
        if (maxHeight == null) {
            maxHeight = input[i];
            maxHeightIndex = i;
        }

    }

    private void setMaxDeep(int[] input, int i) {
        if (lowerElement == Integer.MAX_VALUE)
            return;

        int maxDeepLocal;
        if (i == input.length - 1 && input[i] < input[i - 1]) {
            maxDeepLocal = input[i - 1] - lowerElement;
        } else {
            if (i == input.length - 1) {
                maxDeepLocal = input[i] - lowerElement;
            } else {
                maxDeepLocal = maxHeight - lowerElement;
            }
        }

        if (maxDeepLocal > maxDeep) maxDeep = maxDeepLocal;
    }
}