摘要：
Given two integers n and k, return all possible combinations of k numbers out of 1 ... n. Example: 思路：回溯 阅读全文
摘要：
Given a collection of distinct integers, return all possible permutations. Example: 思路一：二话不说，经典题， 回溯。 思路二： 阅读全文
摘要：
Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers. If such arrangement is not possib 阅读全文
摘要：
You need to construct a string consists of parenthesis and integers from a binary tree with the preorder traversing way. The null node needs to be rep 阅读全文