recursion in mergesort: two recursive calls

Question

private void mergesort(int low, int high) {     //line 1
if (low < high) {                               //line 2
    int middle = (low + high)/2 ;               //li         


        

Answer 1

Regarding your second snippet :

public static void recursionExample(int i){     
    if(i < 3){                                 
        recursionExample(i+1);  // this is called for the last time when i==2, i.e. the
                                // last call is recursionExample(3). When that call 
                                // returns, i is still equal 2, since calling  
                                // recursionExample(i+1) doesn't change the value of the
                                // local variable i of the current method call

        recursionExample(i-1);  // Therefore when this line is first called, i is equal 2
    }                                         
} 

Answer 2

Considering your second snippet, the order of calls is the following (represented as a tree for ease of understanding) :

- recursionExample(0)
  - recursionExample(1)
    - recursionExample(2)
      - recursionExample(3), here no more recursion
      - recursionExample(1)
        ...
    - recursionExample(0)
      ...
  - recursionExample(-1)
    - recursionExample(0)
      ...
    - recursionExample(-2)
      ...