摘要：https://leetcode.com/problems/permutation-sequence/discuss/22507/%22Explain-like-I'm-five%22-Java-Solution-in-O(n) https://www.youtube.com/watch?v=xdvPD1IiyUM The set [1,2,3,...,n] contains a to... 阅读全文

摘要：带返回值的recursion， dfs 阅读全文

摘要：Given a string s, return all the palindromic permutations (without duplicates) of it. Return an empty list if no palindromic permutation could be form. Example 1: Input: "aabb" Output: ["abba", "ba... 阅读全文

摘要：(3)找出1-650中所有的ambiguous number,定义：如果把一个数upside down还是一个有效数的话，这个数就是ambiguous，比如19 -> 61, follow up找到1-n中的这种数 A strobogrammatic number is a number that looks the same when rotated 180 degrees (look... 阅读全文

摘要：You are playing the following Flip Game with your friend: Given a string that contains only these two characters: + and -, you and your friend take turns to flip two consecutive "++" into "--". The g... 阅读全文

摘要：带返回值的dfs recursion 阅读全文

摘要：two things: 带返回值的dfs recursion if(board[3 * (row / 3) + i / 3][ 3 * (col / 3) + i % 3] != '.' && board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] = 阅读全文

摘要：Given a set of words (without duplicates), find all word squares you can build from them. A sequence of words forms a valid word square if the kth row and column read the exact same string, where 0 ≤... 阅读全文

摘要：Given a directed, acyclic graph of N nodes. Find all possible paths from node 0 to node N-1, and return them in any order. The graph is given as follows: the nodes are 0, 1, ..., graph.length - 1. ... 阅读全文

摘要：Numbers can be regarded as product of its factors. For example, 8 = 2 x 2 x 2; = 2 x 4. Write a function that takes an integer n and return all possible combinations of its factors. Note: 1. You ma... 阅读全文

摘要：The method startsWith() is used for checking prefix of a String. It returns a boolean value true or false based on whether the specified string is pre 阅读全文

摘要：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 puzzle. Each... 阅读全文

摘要：You are given a binary tree in which each node contains an integer value. Find the number of paths that sum to a given value. The path does not need t 阅读全文

摘要：public String substring(int startIndex): This method returns new String object containing the substring of the given string from specified startIndex 阅读全文

摘要：not tested yet 阅读全文

摘要：example: 1 1 1 2 for the first pos, we can chose 1 and 2 , skip the two 1s in the middle , the way we skip these 1s is within the for loop, we only ad 阅读全文

摘要：Given a string that contains only digits 0-9 and a target value, return all possibilities to add binary operators (not unary) +, -, or * between the d 阅读全文

摘要：Given an integer array, your task is to find all the different possible increasing subsequences of the given array, and the length of an increasing su 阅读全文

摘要：Design a data structure that supports the following two operations: search(word) can search a literal word or a regular expression string containing o 阅读全文

摘要：再尝试用 isWord boolean 的方式创建 trienode , 做下这道题。 Given a 2D board and a list of words from the dictionary, find all words in the board. Each word must be c 阅读全文