Programming Pearl Chapter 1 11th finding the K-small number from the array

Finding the median indicates that the question is a special case of knowing the question. Finding the number smaller than K and using the Division idea of the Quick Sort, time complexity O (N + n/2 + N/4 ....) = O (N)

Void swap (int * a, int * B) {int temp = * A; * A = * B; * B = temp;} void qselect (int * List, int left, int right, int K) // index is K, not the rank {If (Left = right) return; int key = list [left]; int I = left, j = right + 1; while (I <j) {do {I ++;} while (I <= Right & list [I] <key ); do {J --;} while (list [J]> key); if (I> J) break; swap (& list [I], & list [J]);} swap (& list [left], & list [J]); If (j = k) return; else if (j <k) qselect (list, J + 1, right, k); else qselect (list, left, J-1, k );}