Question

7) Here is the code for the partition function (used by Quick Sort). Explain the purpose of each line of code. int partition (int* vals, int low, int high) { int lowpos = low; low++; while (low <= high) { while (low <= high && vals[low] <= vals [lowpos]) low++; while (high >= low && vals[high) > vals[lowpos]) high--; if (low < high) swap (&vals[low], &vals[high]); swap (&vals[lowpos], &vals[high]); return high;

Answer 1

//7)
int partition(int* vals, int low, int high)
{
   int lowpos =low;//assums leftmost element as pivot
   low++;//now excluding pivot
  
   while(low<=high)//loop runs upto low is less than or equal to high
   {
       while(low<=high && vals[low]<=vals[lowpos])//loop runs upto low is less than or equal to high and value at index low is less than or equal to pivot
       low++;//then increasing low
       while(high>=low &&vals[high]>vals[lowpos])//loop runs upto high is greater than or equal to low and value at index high is greater than pivot
       high--;//then decreasing high
       if(low<high)//if low is less than high
       swap(&vals[low],&vals[high]);//then swapping values at indexes low and high
          
   }
   //finally updating pivot position
   swap(&vals[lowpos],&vals[high]);//swapping values at indexes lowpos and high
   return high;//returning pivot index//or parition index
}