DR_TITI的专栏

一、原题：Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.push(x) -- Push element x onto stack.pop() -- Removes the element on top of the stack.to

一、原题Given an arraynumsofnintegers, are there elementsa,b,cinnumssuch thata+b+c= 0? Find all unique triplets in the array which gives the sum of zero.Note:The solution set must no...

一、原题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?二、分析选用两个指针扫描链表，一个速度快，一个速度慢，若两个指针相遇，说明有环。三、

一原题Find Peak ElementA peak element is an element that is greater than its neighbors.Given an input array where num[i] ≠ num[i+1], find a peak element and return its index.The array m

一、原题Sort List Sort a linked list in O(n log n) time using constant space complexity.二、分析快速排序和归并排序的时间复杂度是O(nlogn)。如果使用归并排序，在使用链表的情况下，不需要重新申请空间存放排序后的数组，可以做到空间复杂度数O(1)。我在这里使用归并排序来排序链表

一、原题Reorder ListGiven 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

一原题Intersection of Two Linked Lists Write a program to find the node at which the intersection of two singly linked lists begins.For example, the following two linked lists:A:

一、原题Binary Tree Preorder TraversalGiven a binary tree, return the preorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3

一、原题：二、分析：三、代码：

一、原题Evaluate Reverse Polish NotationEvaluate the value of an arithmetic expression in Reverse Polish Notation.Valid operators are +, -, *, /. Each operand may be an integer

一、原题Given a string containing digits from2-9inclusive, return all possible letter combinations that the number could represent.A mapping of digit to letters (just like on the telephone buttons) ...