CLRS:median and order statistics

//maximum and minimum     暴力遍历 O(n)

//i-th element dicide and conquer

random_selected_partition     k(all the element samller than value[k] put left of value[k],all tht elenment larger than value[k] put right)

recurrence test

if(i=k)return value[k]

if(i<k)do left partion find i-th

else  do right partion  find i-k th