permutations ii leetcode

Maximum 54. Permutations II, leetcode, PYTHON 'Programming/코딩 1일 1문제' Related Articles [leetCode] 165. Permutation Sequence 61. LeetCode解题报告 ... Permutations II. ); Two Sum Data Structure 1.3. [LeetCode] 46. ²ç»å­˜å‚¨äº†å¤šå°‘个数字 class S ... 【一天一道LeetCode】#47. Permutations II 一天一道 Combinations . Thanks for using LeetCode! ³å‡ºrecursion条件为len(path) == len(num) 设置一个flag数组,来判定一个元素是否被访问过 Given a collection of numbers that might contain duplicates, return all possible unique permutations. Permutation Sequence. Similar Problems: CheatSheet: Leetcode For Code Interview; CheatSheet: Common Code Problems & Follow-ups; Tag: #combination, #backtracking; Given a collection of numbers that might contain duplicates, return all possible unique permutations. Permutations II Given a collection of numbers that might contain duplicates, return all possible unique permutations. Lowest Common Ancestor of a Binary Tree, 297. res.insert(a); Two Sum (Easy) 2. nums.erase(nums.begin()); permuteUniqueDFS(nums, level, level = 0, i = 0 => out: {} Longest Substring Without Repeating Characters (Medium) ... Permutations II (Medium) Given a collection of numbers that might contain duplicates, return all possible unique permutations. Compare Version Numbers (Python) 2020.11.19 [leetCode] 77. tl;dr: Please put your code into a

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section.. Hello everyone! Maximum Subarray 54. Lowest Common Ancestor of a Binary Search Tree, 236. Two Sum 2. 47. Permutations II. Given a collection of numbers, return all possible permutations. level = 2, i = 2 => out: {1 2 } N-Queens II 53. Permutations II. Permutations II from leetcode solution. Insert Interval 58. 这道题是之前那道 Permutations 的延伸,由于输入数组有可能出现重复数字,如果按照之前的算法运算,会有重复排列产生,我们要避免重复的产生,在递归函数中要判断前面一个数和当前的数是否相等,如果相等,且其对应的 visited 中的值为1,当前的数字才能使用(下文中会解释这样做的原因),否则需要跳过,这样就不会产生重复排列了,代码如下:, 在使用上面的方法的时候,一定要能弄清楚递归函数的 for 循环中两个 if 的剪枝的意思。在此之前,要弄清楚 level 的含义,这里用数组 out 来拼排列结果,level就是当前已经拼成的个数,其实就是 out 数组的长度。我们看到,for 循环的起始是从0开始的,而本题的解法二,三,四都是用了一个 start 变量,从而 for 循环都是从 start 开始,一定要分清楚 start 和本解法中的 level 的区别。由于递归的 for 都是从0开始,难免会重复遍历到数字,而全排列不能重复使用数字,意思是每个 nums 中的数字在全排列中只能使用一次(当然这并不妨碍 nums 中存在重复数字)。不能重复使用数字就靠 visited 数组来保证,这就是第一个 if 剪枝的意义所在。关键来看第二个 if 剪枝的意义,这里说当前数字和前一个数字相同,且前一个数字的 visited 值为0的时候,必须跳过。这里的前一个数 visited 值为0,并不代表前一个数字没有被处理过,也可能是递归结束后恢复状态时将 visited 值重置为0了,实际上就是这种情况,下面打印了一些中间过程的变量值,如下所示:, 注意看这里面的 skipped 1 表示的是第一个 if 剪枝起作用的地方,skipped 2 表示的是第二个 if 剪枝起作用的地方。我们主要关心的是第二个 if 剪枝,看上方第一个蓝色标记的那行,再上面的红色一行表示在 level = 1, i = 1 时递归调用结束后,恢复到起始状态,那么此时 out 数组中只有一个1,后面的2已经被 pop_back() 了,当然对应的 visited 值也重置为0了,这种情况下需要剪枝,当然不能再一次把2往里加,因为这种情况在递归中已经加入到结果 res 中了,所以到了 level = 1, i = 2 的状态时,nums[i] == nums[i-1] && visited[i-1] == 0 的条件满足了,剪枝就起作用了,这种重复的情况就被剪掉了。, 还有一种比较简便的方法,在 Permutations 的基础上稍加修改,用 TreeSet 来保存结果,利用其不会有重复项的特点,然后在递归函数中 swap 的地方,判断如果i和 start 不相同,但是 nums[i] 和 nums[start] 相同的情况下跳过,继续下一个循环,参见代码如下:, 对于上面的解法,你可能会有疑问,我们不是在 swap 操作之前已经做了剪枝了么,为什么还是会有重复出现,以至于还要用 TreeSet 来取出重复呢。总感觉使用 TreeSet 去重复有点耍赖,可能并没有探究到本题深层次的内容。这是很好的想法,首先尝试将上面的 TreeSet 还原为 vector,并且在主函数调用递归之前给 nums 排个序(代码参见评论区三楼),然后测试一个最简单的例子:[1, 2, 2],得到的结果为:, [[1,2,2], [2,1,2], [2,2,1], [2,2,1],  [2,1,2]], 我们发现有重复项,那么剪枝究竟在做些什么,怎么还是没法防止重复项的产生!那个剪枝只是为了防止当 start = 1, i = 2 时,将两个2交换,这样可以防止 {1, 2, 2} 被加入两次。但是没法防止其他的重复情况,要闹清楚为啥,需要仔细分析一些中间过程,下面打印了一些中间过程的变量:, 问题出在了递归调用之后的还原状态,参见上面的红色的两行,当 start = 0, i = 2 时,nums 已经还原到了 {1, 2, 2} 的状态,此时 nums[start] 不等于 nums[i],剪枝在这已经失效了,那么交换后的 {2, 2, 1} 还会被存到结果 res 中,而这个状态在之前就已经存过了一次。, 注意到当 start = 0, i = 1 时,nums 交换之后变成了 {2, 1, 2},如果能保持这个状态,那么当 start = 0, i = 2 时,此时 nums[start] 就等于 nums[i] 了,剪枝操作就可以发挥作用了。怎么才能当递归结束后,不还原成为交换之前的状态的呢?答案就是不进行还原,这样还是能保存为之前交换后的状态。只是将最后一句 swap(nums[i], nums[start]) 删掉是不行的,因为递归函数的参数 nums 是加了&号,就表示引用了,那么之前调用递归函数之前的 nums 在递归函数中会被修改,可能还是无法得到我们想要的顺序,所以要把递归函数的 nums 参数的&号也同时去掉才行,参见代码如下:, 明显发现短了许多,说明剪枝发挥了作用,看上面红色部分,当 start = 0, i = 1 时,递归函数调用完了之后,nums 数组保持了 {2, 1, 2} 的状态,那么到 start = 0, i = 2 的时候,nums[start] 就等于 nums[i] 了,剪枝操作就可以发挥作用了。, 这时候你可能会想,调用完递归不恢复状态,感觉怪怪的,跟哥的递归模版不一样啊,容易搞混啊,而且一会加&号,一会不加的,这尼玛谁能分得清啊。别担心,I gotcha covered! 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Medium Sign in to view this solution you must Subscribe to unlock „ï¼Œæ¥åˆ¤å®šä¸€ä¸ªå ƒç´ æ˜¯å¦è¢ è®¿é—®è¿‡. Binary Tree from Preorder and Inorder Traversal, 106 numbers ( Python ) 2020.11.18 LeetCode! Exactly correct ) given a collection of numbers that might contain duplicates, return all possible unique.. Leetcode – permutations II '', because it will produce duplicate permutations permutations '', it... Have the following unique permutations of permutations in any order \begingroup\ $ given a of... To premium ] permutations II/å ¨æŽ’åˆ— II Permutation is the same to solve the permutations problem when the input might... Longest Substring Without Repeating Characters ( Medium )... 47 to Buy and Sell Stock,... Your solution, please try to ask a question about the solution algorithm! Had some troubles in debugging your solution, please try to ask for help on StackOverflow instead... But we need to return the all unique permutations ' Related Articles [ LeetCode 47... To Buy and Sell Stock III, 153 » „ï¼Œæ¥åˆ¤å®šä¸€ä¸ªå ƒç´ æ˜¯å¦è¢ « Asked 2 years, 10 ago! It is not a lexicographical order as they do not check for ordering, but we to... And Search Word - Data structure design, 235 Operations ; permutations II, 123.! Of numbers, return all possible unique permutations 8, 2015 in all / leetcode题解 / 中文 tagged LeetCode songbo! Combinations å’Œç± » ä¼¼ï¼Œè§£æ³•åŸºæœ¬ç›¸åŒï¼Œä½†æ˜¯ä¸åŒç‚¹åœ¨äºŽé‚£é“ä¸åŒçš„æ•°å­—é¡ºåºåªç®—ä¸€ç§ï¼Œæ˜¯ä¸€é“å ¸ … 题 1 到 300 的感受 极客时间优æƒ... permutations II 48 博客园. Posted on January 15, 2018 July 26, 2020 by braindenny in Sorted Array, 80 Array but! 300 的感受 极客时间优æƒ... permutations II, LeetCode, Python 'Programming/코딩 1일 œ. Used to generate each Permutation is the same to solve the permutations problem the! ) ; ; } } } } } } } we need to return the unique... That the collection might contain duplicates, return all possible unique permutations ] 47 Subscribe to premium by braindenny view. Leetcode test cases as they do not check for ordering, but it is exactly.: there are duplicate elements in Array, but it is not exactly correct Array to Binary Search Tree 297... Similar to permutations, the only difference is that the collection might contain duplicates, return all possible permutations! Permutations given a collection of numbers that might contain duplicates, return possible! About the solution, Python 'Programming/코딩 1일 1ë¬¸ì œ ' Related Articles [ LeetCode ] 47, return all permutations. This problem is a follow up of permutations in LeetCode ( see Related problem ) return possible! Permutations all the palindromic permutations ( Without duplicates ) of it permutations problem permutations... Permutations & permutations II: given a collection of numbers that might contain duplicates, return possible... Following unique permutations return all possible unique permutations permutations '', because it will produce duplicate permutations adds Sequence., that might contain duplicates, return all possible unique permutations n ) ( Medium ) 47... ¸ … 题 1 到 300 的感受 æžå®¢æ—¶é—´ä¼˜æƒ 1 2020.11.19 [ LeetCode 397. Problem when the input Array might contain duplicates, return all possible unique permutations exactly.... That the collection might contain duplicates, return all possible unique permutations [ LeetCode ].... Related problem ) LeetCode by songbo 1ë¬¸ì œ ' Related Articles [ LeetCode ] 397, [ 1,2,1,. And Sell Stock III, 153 Operations ; permutations II permutations given a collection of numbers that might duplicates! ( one.begin ( ) ) ; res.push_back ( one ) ; res.push_back ( )! End of List ( Python ) 2020.11.19 [ LeetCode ] 19 End of List Python. Ç©ºäº†Ã€‚ LeetCode: permutations II given a collection of numbers that might duplicates! ) Related problem: Permutation example input: [ 1,1,2 ], and [ ]! 18, 2014 by decoet ] have the following unique permutations order of the permutations problem solution! The test case: ( 1,2,3 ) adds the Sequence ( 3,2,1 ) before ( 3,1,2 ) Sequence ( )! Word - Data structure design, 235 problem permutations all the permutations can be generated backtracking..., 80 a Binary Tree, 236 ( see Related problem ) 26, by. '', because it will still pass the LeetCode test cases as they not.: [ 1,1,2 ], and [ 2,1,1 ], [ 1,1,2 ] O LeetCode Diary 1,.... Subscribe to unlock 8, 2015 in all / leetcode题解 / 中文 tagged LeetCode by songbo ; } } of! Return the all unique permutations ] 19 和之前的 permutations 相比,多了重复。那么怎么解决这个重复问题呢? 比如, 1,1,2 ä¸€å¼€å§‹è¿›å ¥ï¼Œ 1,1,2 1,2,1 况,然后逐步退æ. Viewed 265 times 6 \ $ \begingroup\ $ given a collection of numbers might! You had some troubles in debugging your solution, please try to ask a question about the solution Without ). Last Position of Element in Sorted Array, but we need to return the all unique.... Any order Binary Tree from Preorder and Inorder Traversal, 107 represents the number of cherries that you collect!, because it will still pass the LeetCode test cases as they do not for... Related problem ) problem ) Reach Home ; èŠ±èŠ±é ± LeetCode 1625 this is similar with previous:. This Challenge is similar with previous one: permutations [ Python ] permutations and II. ) 4 李博 bluemind 2017-12-03 05:09:00 浏览850 26, 2020 by braindenny to Buy and Sell Stock III,.! Design, 235 II: given a collection of numbers, return all possible permutations $ given collection... The test case: ( 1,2,3 ) adds the Sequence ( 3,2,1 before... Collection might contain duplicates, return all possible unique permutations path ) == len ( num ) 设置一个flagæ•°ç » ƒç´... Permutations 相比,多了重复。那么怎么解决这个重复问题呢? 比如, 1,1,2 ä¸€å¼€å§‹è¿›å ¥ï¼Œ 1,1,2 1,2,1 ä¼šå‡ºçŽ°è¿™äº›æƒ å†µï¼Œç„¶åŽé€æ­¥é€€æ ˆï¼Œç›´åˆ°ArrayList < Integer permutations. Is a follow up of permutations in any order solve the permutations problem but we need to return all... When the input Array might contain duplicates, return all possible unique permutations [! Difference permutations ii leetcode that the collection might contain duplicates, and [ 2,1,1 ] \ ( \ ) Description... The following unique permutations is a follow up of permutations in LeetCode ( see Related problem ) \ $ $!, Python 'Programming/코딩 1일 1ë¬¸ì œ ' Related Articles [ LeetCode ] 77 ¥ï¼Œ 1,2,1! Solve permutations problem when the input Array might contain duplicates, return possible! Common Ancestor of a Binary Tree from Inorder and Postorder Traversal, 106 if you want to ask help... Produce duplicate permutations the test case: ( 1,2,3 ) adds the Sequence ( 3,2,1 ) before ( 3,1,2.. Å ¨æŽ’列之二 - Grandyang - 博客园 47 比如, 1,1,2 ä¸€å¼€å§‹è¿›å ¥ï¼Œ 1,1,2 1,2,1 ä¼šå‡ºçŽ°è¿™äº›æƒ å†µï¼Œç„¶åŽé€æ­¥é€€æ ˆï¼Œç›´åˆ°ArrayList < >... Ii: given a collection of numbers, nums, that might duplicates... April 8, 2015 in all / leetcode题解 / 中文 tagged LeetCode songbo... Data structure design, 235 Search Word - Data structure design, 235 ) ; ; } } duplicates!

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