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leetcode Problem 13： Given a roman numeral, convert it to an integer. Input is guaranteed to be within the range from 1 to 3999. 题目：将罗马数字转换成整数  首先要了解罗马数字表示法，基本字符有7个：I，V，X，L，C，D，M，分别表示1，5，

题目： Given an integer n, return the number of trailing zeroes in n!. Note: Your solution should be in logarithmic time complexity. 乍一看，这确实不难，很简单的做法是先求n！嘛，然后求0的个数。结果是没问题，但是时间复杂度不符合要求，求n!就要O

题目： Given an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times. You may assume that the array is non-empty and the majority e

题目 Pascal's triangle  Given numRows, generate the first numRows of Pascal's triangle. For example, given numRows = 5, Return [ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1] ]

题目： You are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adjacen

题目： Reverse bits of a given 32 bits unsigned integer. For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as 00

题目：Reverse digits of an integer. Example1: x = 123, return 321 Example2: x = -123, return -321 Test cases had been added to test the overflow behavior. 本题很简单，唯一值得注意的点是反转之后要做溢出检查，有两种方式，一可以每

leetcode 28： Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack. 本题属于字符串匹配问题，用KMP算法 KMP算法：举例来说，有一个字符串"BBC ABCDAB ABCDABCDABDE"，我想知道，里

下一个字典序 Next Permutationleetcode 31题目描述：Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers. If such arrangement is not possible, it must