不使用ArrayList将2D数组转换为1D Array

Question

Create Function for Convert 2d array into 1D array

But at Declaration time the size of 1D array how to give size to the new 1D array

int[] convert(int[][] input){
    int[] result;
    int z=0;
    for(int row=0;row<input.length;row++) {
        for(int col=0;col<input[row].length;col++) {
            result[z]=input[row][col];
            z++;
        }
    }
    return result;/* Error comes here For Initialization. How to initialize before Knowing size*/
}

Answer 1

if rows and columns are balanced

int result[] = new int[input.length * input[0].length];

otherwise, you have to loop through the whole array while keeping a count of length

int len = 0;
for(int[] a : input){
    len+=a.length;
}
int[] result = new int[len];

Answer 2

您可以通过这种方式简单地计算大小（即行数* 列数 ）：

int[] result = new int[input.length * input[0].length] ;

Answer 3

1)If it is rectangular 2D array, compute the size this way

int array[]  = new int[input.length * input[0].length];

2)If it is not rectangular, iterate through each row and add the length of each sub-array

int size = 0;
for(int i=0;i<input.length;i++){
 size += input[i].length;
}

Answer 4

Or you could just use streams with out to have to take care of size by yourself:

int[] convert(int[][] input){    
    return Stream.of(input).flatMapToInt(x -> Arrays.stream(x)).toArray();
}