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第二遍做leetcode 中的回溯法， 发现不光没有更好的理解，甚至遗忘了很多。 所以今天觉得做一篇有关回溯法的总结 首先，回溯法的基本思想：从一条路往前走，能进则进，不能进则退回，换一条路再试 回溯法的基本定义和概念 首先要明确下面三个概念 1约束函数：约束函数是根据题意定出， 通过描述合法解的一般特征用于去除不合法的解，从而避免继续搜索出这个不合法解的剩余部分 2状态空间树 状态空间树是一个对...

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telephone buttons) is give...

Given a string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s. Example: Input: “aab” Output: [ [“aa”,“b”], [“a”,“a”,“b”] ] ...

Given a binary tree and a sum, find all root-to-leaf paths where each path’s sum equals the given sum. Note: A leaf is a node with no children. Example: Given the below binary tree and sum = 22, 5 ...

Given a collection of integers that might contain duplicates, nums, return all possible subsets (the power set). Note: The solution set must not contain duplicate subsets. Example: Input: [1,2,2] Outp...

Given a set of distinct integers, nums, return all possible subsets (the power set). Note: The solution set must not contain duplicate subsets. Example: Input: nums = [1,2,3] Output: [ [3], [1], [2], ...

Given two integers n and k, return all possible combinations of k numbers out of 1 … n. Example: Input: n = 4, k = 2 Output: [ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4], ] 看到这种排列的题目 第一想到就是backtracking ...

Given a collection of numbers that might contain duplicates, return all possible unique permutations. Example: Input: [1,1,2] Output: [ [1,1,2], [1,2,1], [2,1,1] ] 思路 backtracking 和第36题一样 但是多一个去重 首先将数...

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target. The same repeate...