At the start of each iteration k of the for loop, the subarray A[p..k-1] contains the (k-p) smallest elements of A [p..r] in sorted order. At the start of each iteration i of the for loop, the subarray A[p..r] contains the (i-p) smallest elements of A[p..r] in sorted order. At the start of each iteration k of the for loop, the subarray A[1..k] contains the k smallest elements of A in sorted order. At the start of each iteration k of the for loop, the subarray A[k..r] contains the (r-k+1) largest elements of A[p..r] in sorted order.