展平锯齿状2D阵列

Question

I have an assignment that asks me to flatten a 2D array into a single array.

Here's what I have so far:

public static int[] flatenArray(int [][] a){
    //TODO
    int length = 0;

    for(int y = 0; y < a.length; y++){
        length += a[y].length;
    }

    int[] neu = new int[length];

    int x = 0;
    for (int i = 0; i < a.length; i++){
        for(int j = 0; j < a[0].length; j++){
            neu[x] = a[i][j];
            x++;
        }
    }
    return neu;
}

When doing a JUnit Test for the following test case

assertArrayEquals(new int[] {1,2,3,4,5,6,7,8,9,10,11},Ass06.flatenArray(new int[][] {{1,2,3},{4,5,6},{7,8,9,10,11}}));

I get the following error:

arrays differed at element[9]; expected <10> but was <0>

Somehow at the point where the array length of the 3rd "inner array" surpasses 3, the last 2 numbers ("10, 11") are not copied into the new array.

Answer 1

There are multiple ways to solve this this, but it all comes down to you counting things wrong.

In a new int[1] , the first element is index 0. In an array of 1 element, .length will return 1 , but there will be no array[1] . That's why you're missing the the count by 1.