The set [1,2,3,…,n] contains a total of n! unique permutations. By listing and labeling all of the permutations in order,We get the following sequence (ie, for n = 3): "123" "132" "213" "231" "312" "3…

The set [1,2,3,…,n] contains a total of n! unique permutations. By listing and labeling all of the permutations in order,We get the following sequence (ie, for n = 3): "123" "132" "213" "231" "312" "3…

问题: 对于给定序列1...n,permutations共同拥有 n!个,那么随意给定k,返回第k个permutation.0 < n < 10. 分析: 这个问题要是从最小開始直接到k,预计会超时,受10进制转换为二进制的启示,对于排列,比方 1,2,3 是第一个,那么3!= 6,所以第6个就是3,2,1.也就是说,从開始的最小的序列開始,到最大的序列,就是序列个数的阶乘数.那么在1,3 , 2的时候呢?调整一下,变成2,1,3,就能够继续. 实现: int getFactorial(int…

The gray code is a binary numeral system where two successive values differ in only one bit. Given a non-negative integer n representing the total number of bits in the code, print the sequence of gray code. A gray code sequence must begin with 0. Fo…

Sort a linked list in O(n log n) time using constant space complexity. 思路: 用归并排序.设输入链表为S,则先将其拆分为前半部分链表A,后半部分链表B.注意,要把A链表的末尾置为NULL.即要把链表划分为两个独立的部分,防止后面错乱. #include <iostream> #include <vector> #include <algorithm> #include <queue> #…

1. Next Permutation 实现C++的std::next_permutation函数,重新排列范围内的元素,返回按照 字典序 排列的下一个值较大的组合.若其已经是最大排列,则返回最小排列,即按升序重新排列元素.不能分配额外的内存空间. void nextPermutation(vector<int>& nums) { next_permutation(nums.begin(), nums.end()); } 全排列 Permutation 问题已经被古人研究透了,参见 W…

Given a collection of integers that might contain duplicates, S, return all possible subsets. Note: Elements in a subset must be in non-descending order. The solution set must not contain duplicate subsets. For example,If S = [1,2,2], a solution is:…

今天开始,回溯法强化阶段. Given a 2D board and a word, find if the word exists in the grid. The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same letter cell…

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"], ["a","a","…

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: "((()))", "(()())", "(())()", "()(())", "()()()" 思路:产生所有…