Evaluate the value of an arithmetic expression in Reverse Polish Notation.

Valid operators are + , -, *, / .Each operand may be an integer or another expression.

Some examples :
[“2”, “1”, “+”, “3”, ““] -> ((2 + 1) 3) -> 9
[“4”, “13”, “5”, “/“, “+”] -> (4 + (13 / 5)) -> 6

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.

题意：

　　在二维平面上给定n个坐标点，找落在同一条直线上点的个数，并找出落在同一直线上点最多的个数。

Sort a linked list in O(n log n) time using constant space complexity.

题意：

　　在 O(n log n)的时间复杂度内，在恒定的空间复杂度内，排序单链表。

Sort a linked list using insertion sort.

题意：

　　使用插入排序对单链表进行排序。

Given a binary tree, return the postorder traversal of its nodes’ values.

1
2
3
4
5
6
7
8
9

For example :
Given binary tree{ 1,#,2,3 },

             1
               \
               2
              /
             3
return[3, 2, 1].

Given a binary tree, return the preorder traversal of its nodes’ values.

1
2
3
4
5
6
7
8
9

For example :
Given binary tree{ 1,#,2,3 },

       1
        \
          2
         /
       3
return[1, 2, 3].

Given a singly linked list L : L0→L1→…→Ln - 1→Ln,
reorder it to : L0→Ln→L1→Ln - 1→L2→Ln - 2→…

You must do this in - place without altering the nodes’ values.

For example,
Given{ 1,2,3,4 }, reorder it to{ 1,4,2,3 }.

Given a linked list, return the node where the cycle begins.If there is no cycle, return null.

Note: Do not modify the linked list.

141. Linked List Cycle

Given a linked list, determine if it has a cycle in it.

Follow up :
Can you solve it without using extra space ?

138. Copy List with Random Pointer

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.