--- 自由在高处

题目：Given a collection of intervals, merge all overlapping intervals.For example,Given [1,3],[2,6],[8,10],[15,18],return [1,6],[8,10],[15,18].思路：先是进行排序，从前往后按照第一个数字进行排序。这个时候一个小技巧就是把第一个区间保存

题目：Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.Note:You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold

题目：Follow up for "Unique Paths":Now consider if some obstacles are added to the grids. How many unique paths would there be?An obstacle and empty space is marked as 1 and 0 respectively in the

题目：A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).The robot can only move either down or right at any point in time. The robot is trying to reach the b

题目：Implement pow(x, n).思路：递归首先把极限情况考虑，直接返回，接下来就是负指数的处理。最后考虑下指数是奇数还是偶数，递归调用。(注意，这种类型题目务必判断是否越界)代码：class Solution {public: double myPow(double x, int n) {

题目：Divide two integers without using multiplication, division and mod operator.思路：注意越界问题。比如： -2147483648/1=-2147483648 -2147483648/-1=2147483647最主要的应该是如何进行除法吧，思路如下：a/b，a-b --  a-2*b --

题目：计算X均方根思路：二分法代码：class Solution {public: int mySqrt(int x) { if(x<=0) return 0; if(x<4) return 1; if(x/2>=46340){ return binaryLowInt(x

题目：Given n, how many structurally unique BST's (binary search trees) that store values 1...n ?For example  ,  Given n = 3, there are a total of 5 unique BST's. 1 3 3 2

题目：Given n, generate all structurally unique BST's (binary search trees) that store values 1...n.For example,Given n = 3, your program should return all 5 unique BST's shown below. 1

题目：Given an index k, return the kth row of the Pascal's triangle.For example, given k = 3,Return [1,3,3,1].思路：递推思路很明确，一层一层递推，并且只需要设立一个数组，本题不难。只需要注意一个解题公式即可代码：class Solution1 {public://f

题目：Reverse digits of an integer.Example1: x = 123, return 321Example2: x = -123, return -321思路：迭代计算，保存末尾值。注意一开始的负号第一个需要注意的就是判断最大值最小值，尤其是最小值，这一点在后面的求解除法中非常明显。代码：class Solution {publi

题目：Given a binary tree, find its minimum depth.The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.思路：深搜+广搜深搜的方法和之前一样。主要讲一下广搜的

题目：Given two numbers represented as strings, return multiplication of the numbers as a string.思路：重新编写乘法、加法函数尤其注意究竟是数字操作还是字符本身操作，在好几个地方被卡主，都是保存为string的时候没有能够保存正确。代码：class Solution {pub

题目：Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.For example, given candidate set 2,3,6,7 and target 7,

题目：Given a binary tree, find its maximum depth.The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.思路：深搜如果节点为空，返回0,；如果不为空，要看是否

题目：Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.For example,If n = 4 and k = 2, a solution is:[ [2,4], [3,4], [2,3], [1,2], [1,3], [1,

题目：Given a string s, partition s such that every substring of the partition is a palindrome.Return the minimum cuts needed for a palindrome partitioning of s.For example, given s = "aab",Ret

题目：Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.Note: You can only move either down or rig

题目：Given a string s, partition s such that every substring of the partition is a palindrome.Return all possible palindrome partitioning of s.For example, given s = "aab",Return [ ["aa","b

题目：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 (

题目：Given a collection of numbers that might contain duplicates, return all possible unique permutations.For example,[1,1,2] have the following unique permutations:[1,1,2], [1,2,1], and [2,

题目：Follow up for "Search in Rotated Sorted Array":What if duplicates are allowed ? Would this affect the run-time complexity? How and why?Write a function to determine if a given target is i

题目：Write a function to find the longest common prefix string amongst an array of strings.思路：最长公共前缀长度至少不会超过第一个数组的长度。并且竖向扫描，只要某一行的某一位不等于第一行对应的符号，就退出，否则就说明程序执行到最后。代码：class Solution {publ

题目：Given two words word1 and word2, find the minimum number of steps required to convert word1 to word2. (each operation is counted as 1 step.)You have the following 3 operations permitted o

题目：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.        

题目：Given a collection of numbers, return all possible permutations.For example,[1,2,3] have the following permutations:[1,2,3], [1,3,2], [2,1,3], [2,3,1], [3,1,2], and [3,2,1].思路：使用回

题目：Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:   每一行递增；每一行第一个数字比前一行最后一个数字大。 [1, 3, 5, 7], [10, 11, 16, 20], [23,

题目：Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.You may assume no duplicates in the arr

题目：Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have ex

题目：Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.For example,Given the following matrix:[ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ]]

题目：Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.For example,Given n = 3,You should return the following matrix:[ [ 1, 2, 3 ], [ 8, 9, 4 ],

题目：The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.Given an integer n, return all distinct solutions to the n-queens puz

题目：Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.For example, given n = 3, a solution set is: "((()))", "(()())", "(())()", "()(())",

题目：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

题目：Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.Each number in C may only be used once in the combinat

题目：Given a linked list, swap every two adjacent nodes and return its head.Given 1->2->3->4, you should return the list as 2->1->4->3.思路：设立tail作为下一个list前一个结点，所以每次判断当前和之后是否为空    看了一下思路，立即ACCEP

题目给出一些非重叠区间，插入一个新区间有[1,3],[6,9], 插入 [2,5] 结果为 [1,5],[6,9].有[1,2],[3,5],[6,7],[8,10],[12,16], 插入 [4,9] 结果为 [1,2],[3,10],[12,16].思路：大致三种情况主要注意区间范围的限制。代码class Solution

题目：Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number. 1 / \ 2 3Return the sum = 12 + 13 = 25.思路：递归首先有好几种思路，本程序写的是从顶端到本结点的一个

题目：Given a non-negative number represented as an array of digits, plus one to the number.string1=“1213”，加1之后string=“1214”.思路：    转化+细节实现。代码：class Solution {public: vector plusOne(vect

题目：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).For example,Given [5, 7, 7