摘要：
This problem seems to be tricky at first glance. However, if you know Morris traversal, it is just the preorder case of Morris traversal and the code ... 阅读全文
摘要：
There are many merge-sort solutions at the forum, but very few quicksort solutions. So I post my accepted quicksort solution here.Well, after reading ... 阅读全文
摘要：
This is a typical DP problem. Suppose the minimum path sum of arriving at point(i, j)isS[i][j], then the state equation isS[i][j] = min(S[i - 1][j], S... 阅读全文
摘要：
Well, this problem is similar toUnique Paths. The introduction of obstacles only changes the boundary conditions and make some points unreachable (sim... 阅读全文
摘要：
This is a fundamental DP problem. First of all, let's make some observations.Since the robot can only move right and down, when it arrives at a point,... 阅读全文
摘要：
Well, this problem has a naive solution, which is to sort the array in descending order and return thek-1-th element. However, sorting algorithm gives... 阅读全文
摘要：
To be honest, this problem is designed to let you use stacks. However, I don't. In fact, you only need to keep a flagand switch it between falseandtru... 阅读全文
摘要：
Well, I do not see what this problem is for. The same code of Binary Tree Level Order Traversal can be used here. The only difference is that we shoul... 阅读全文
摘要：
A classic tree traversal problem. I share my two solutions here: BFS and DFS.BFS: 1 vector> levelOrder(TreeNode *root) { 2 vector> levels;... 阅读全文
摘要：
This is a fundamental and yet classic problem. I share my three solutions here:Iterative solution using stack ---O(n)time andO(n)space;Recursive solut... 阅读全文
摘要：
This is a fundamental and yet classic problem. I share my three solutions here:Iterative solution using stack ---O(n)time andO(n)space;Recursive solut... 阅读全文
摘要：
This is a fundamental and yet classic problem. I share my three solutions here:Iterative solution using stack ---O(n)time andO(n)space;Recursive solut... 阅读全文
摘要：
Well, the basic idea is fairly straightforward. We maintain a mappingmpfrom a value innumsto its position (index)i. Each time we meet an unseen value,... 阅读全文
摘要：
This problem is a little tricky at first glance. However, if you have finished theHouse Robber problem, this problem can simply bedecomposed into two ... 阅读全文
摘要：
Well, have you solved thenextPermutationproblem? If so and you have handled the cases of duplicates at that problem, your code can be used in this pro... 阅读全文
摘要：
Well, have you solved thenextPermutationproblem? If so, your code can be used in this problem. The idea is fairly simple:sortnumsin ascending order, a... 阅读全文
摘要：
Well, in fact the problem of next permutation has been studied long ago. From theWikipedia page, in the 14th century, a man named Narayana Pandita giv... 阅读全文