A.2#3#4#1#*+- B.2#3#4#+*1#- C.2#3#4#*+1#- D.-+*2#3#4#1#
A.top++;s[top]=x; B.s[top]=x;top++; C.top--;s[top]=x; D.s[top]=x;top--;
A.O(n) B.O(√n) C.O(nlog2n) D.O(n2)