Simple and readable solution

```
public int[] TwoSum(int[] numbers, int target) {
for(int i=0,j=numbers.Length-1;i<j;)
{
int sum = numbers[i] + numbers[j];
if(sum == target) return new int[] {++i, ++j};
else if(sum < target) i++;
else j--;
}
return new int[]{0,0};
}
```