Evaluate Reverse Polish Notation 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”, “/”, […]
Count and Say The count-and-say sequence is the sequence of integers beginning as follows: 1, 11, 21, 1211, 111221, … 1 is read off as “one 1” or 11. 11 is read off as “two 1s” or 21. 21 is read off as “one 2, then one 1” or 1211. […]
Letter Combinations of a Phone Number Given a digit string, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telephone buttons) is given below. Input:Digit string “23” Output: [“ad”, “ae”, “af”, “bd”, “be”, “bf”, “cd”, “ce”, “cf”]. Note: Although […]
Remove Duplicates from Sorted List Given a sorted linked list, delete all duplicates such that each element appear only once. For example, Given 1->1->2, return 1->2. Given 1->1->2->3->3, return 1->2->3. tag: linked list 简单题，但要注意两点： 1. if 语句条件的判断顺序为从左到右，所以要把判断P为空放在左面先判断，然后再判断p->val == head->val 2. 在函数开始时，把head拷贝给re作为返回元素，head在操作中会被移动。当然，另一个好习惯是把head拷贝成p，然后操作p，最后返回head。 /** * Definition for singly-linked list. * struct ListNode […]
Excel Sheet Column Title Given a positive integer, return its corresponding column title as appear in an Excel sheet. For example: 1 -> A 2 -> B 3 -> C … 26 -> Z 27 -> AA 28 -> AB Credits: Special thanks to @ifanchu for adding this problem and […]
Regular Expression Matching Implement regular expression matching with support for ‘.’ and ‘*’. ‘.’ Matches any single character. ‘*’ Matches zero or more of the preceding element. The matching should cover the entire input string (not partial). The function prototype should be: bool isMatch(const char *s, const char *p) Some […]
Search for a Range Given a sorted array of integers, find the starting and ending position of a given target value. Your algorithm’s runtime complexity must be in the order of O(log n). If the target is not found in the array, return [-1, -1]. For example, Given [5, 7, […]
Pascal’s Triangle II Given an index k, return the kth row of the Pascal’s triangle. For example, given k = 3, Return [1,3,3,1]. Note: Could you optimize your algorithm to use only O(k) extra space? tags: array 动态规划中，如果我们只要某一行的规划矩阵的值，我们每必要存下整个矩阵，因为求解某一行的矩阵的值时我们只需要上一行矩阵的值（对于本题来说），所以我们只需记录上一行矩阵的值即可。 class Solution { public: vector<int> getRow(int rowIndex) { vector<int> row; row.push_back(1); if(rowIndex […]
Two Sum Given an array of integers, find two numbers such that they add up to a specific target number. The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned […]
3Sum Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero. Note: Elements in a triplet (a,b,c) must be in non-descending order. (ie, […]
