MaxSubarraySumTest.java

package com.company.MaxSubarraySum;

import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class MaxSubarraySumTest {
    @Test
    public void testEmptyArray() throws Exception {
        assertEquals("Empty arrays should have a max of 0", 0, MaxSubarraySum.sequence(new int[]{}));
    }

    @Test
    public void testExampleArray() throws Exception {
        assertEquals("Example array should have a max of 6", 6, MaxSubarraySum.sequence(new int[]{-2, 1, -3, 4, -1, 2, 1, -5, 4}));
    }

    @Test
    public void testNegativeExampleArray() throws Exception {
        assertEquals("Example array with all negative values should have a max of 0", 0, MaxSubarraySum.sequence(new int[]{-2, -1, -3, -4, -1, -2, -1, -5, -4}));
    }

    @Test
    public void testCompleteArray() throws Exception {
        assertEquals("Should work on this too", 155, MaxSubarraySum.sequence(new int[]{7, 4, 11, -11, 39, 36, 10, -6, 37, -10, -32, 44, -26, -34, 43, 43}));
    }

    @Test
    public void testRandomArrays() throws Exception {
        for (int i = 0; i < 50; i++) {
            int[] rand = randArr((int) (Math.random() * 10 + 50));
            assertEquals("Random array solution not as expected: ", solution(rand), MaxSubarraySum.sequence(rand));
        }
    }

    private int[] randArr(int size) {
        int[] rand = new int[size];
        for (int i = 0; i < size; i++) rand[i] = (int) (Math.random() * 60 - 30);
        return rand;
    }

    private int solution(int[] arr) {
        int m = 0, a = 0, s = 0;
        for (int e : arr) {
            s += e;
            m = Math.min(s, m);
            a = Math.max(a, s - m);
        }
        return a;
    }
}