Question

What does the following code fragment print? Explain the result?

int [] a = new int[10];

for (int i = 0; i < 10; i++)

   a[i] = 9 - i;

for (int i = 0; i < 10; i++)

   a[i] = a[a[i]];

for (int i = 0; i < 10; i++)

   System.out.println(a[i]);

Answer 1

0
1
2
3
4
4
3
2
1
0

int [] a = new int[10];     // initializes an array of 10 integers
for (int i = 0; i < 10; i++)    // loop through each element in array
    a[i] = 9 - i;       // set 9-i for all elements
// array a after first for loop is
// 9, 8, 7, 6, 5, 4, 3, 2, 1, 0
for (int i = 0; i < 10; i++)    // loop through each element again
    a[i] = a[a[i]]; // set a[i] to a[a[i]]
// a[0] => a[a[0]] = a[9] = 0
// a[1] => a[a[1]] = a[8] = 1
// a[2] => a[a[2]] = a[7] = 2
// a[3] => a[a[3]] = a[6] = 3
// a[4] => a[a[4]] = a[5] = 4
// a[5] => a[a[5]] = a[4] = 4
// a[6] => a[a[6]] = a[3] = 3
// a[7] => a[a[7]] = a[2] = 2
// a[8] => a[a[8]] = a[1] = 1
// a[9] => a[a[9]] = a[0] = 0
for (int i = 0; i < 10; i++)
    System.out.println(a[i]);
// finally, printed array is 0 1 2 3 4 4 3 2 1 0