Problem: Given n points on a 2D plane, find the maximum number of points that lie on the same straight line. Suppose that the structure Point is already defined in as following: /** * Definition for a point. * struct Point { * int x; * int y; * Point…

Max Points on a Line 题目描述: Given n points on a 2D plane, find the maximum number of points that lie on the same straight line. 解题思路: 1.首先由这么一个O(n^3)的方法,也就是算出每条线的方程(n^2),然后判断有多少点在每条线上(N).这个方法肯定是可行的,只是复杂度太高2.然后想到一个O(N)的,对每一个点,分别计算这个点和其他所有点构成的斜率,具有相同斜率最…

Problem Link: http://oj.leetcode.com/problems/interleaving-string/ Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2. For example, Given: s1 = "aabcc", s2 = "dbbca", When s3 = "aadbbcbcac", return t…

Problem link: http://oj.leetcode.com/problems/reverse-words-in-a-string/ Given an input string, reverse the string word by word. For example, Given s = "the sky is blue", return "blue is sky the". LeetCode OJ supports Python now! The s…

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line. 思路: 自己脑子当机了,总是想着斜率和截距都要相同.但实际上三个点是一条直线的话只要它们的斜率相同就可以了,因为用了相同的参照点,截距一定是相同的. 大神的做法: 对每一个点a, 找出所有其他点跟a的连线斜率,相同为同一条线,记录下通过a的点的线上最大的点数. 找出每一个点的最大连线通过的点数. 其…

Given n points on a 2D plane, find the maximum number of points that lie on the same straight line. 题解: 思路比较简单,每条直线都可以表示为y=kx+b,所以对于任意三点,如果它们共线,那么它们中任意两点的斜率都相等. 所以就遍历points数组,对其中的每一个元素计算它和位于它后面的数组元素的斜率并保存在一个hashmap中. 这个hashmap的键就是两点构成直线的斜率,值就是和当前元素po…

Problem Link: http://oj.leetcode.com/problems/balanced-binary-tree/ We use a recursive auxilar function to determine whether a sub-tree is balanced, if the tree is balanced, it also return the depth of the sub-tree. A tree T is balanced if the follow…

Problem Link: http://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/ Linear Time Solution We try to solve this problem in O(n) time in the help of the algorithm in Best Time to Buy and Sell Stock, which can return the max profit by give…

Problem Link: http://oj.leetcode.com/problems/binary-tree-maximum-path-sum/ For any path P in a binary tree, there must exists a node N in P such that N is the ancestor node of all other nodes in P. We call such N as the root of P, or P roots at N. T…

Problem Link: http://oj.leetcode.com/problems/longest-consecutive-sequence/ This problem is a classical problem where we can reduce the running time by the help of hash table. By given a list of numbers, we can find the longest consecutive sequence b…

Problem link: http://oj.leetcode.com/problems/candy/ Suppose we are given an array R[1..N] that are ratings of N children. Let C[1..N] be a new array where C[i] is the number of candies for i-th child. From the description, C[i] should meet following…

Problem link: http://oj.leetcode.com/problems/reorder-list/ I think this problem should be a difficult problem, since it requries three classic algorithms on the single-linked list: Split a single-linked list into halves Reverse a single-linked list…

Problem Link: https://oj.leetcode.com/problems/validate-binary-search-tree/ We inorder-traverse the tree, and for each node we check if current_node.val > prev_node.val. The code is as follows. # Definition for a binary tree node # class TreeNode: #…

Problem Link: https://oj.leetcode.com/problems/recover-binary-search-tree/ We know that the inorder traversal of a binary search tree should be a sorted array. Therefore, we can compare each node with its previous node in the inorder to find the two…

Problem Link: https://oj.leetcode.com/problems/same-tree/ The following recursive version is accepted but the iterative one is not accepted... # Definition for a binary tree node # class TreeNode: # def __init__(self, x): # self.val = x # self.left =…

Problem Link: https://oj.leetcode.com/problems/symmetric-tree/ To solve the problem, we can traverse the tree level by level. For each level, we construct an array of values of the length 2^depth, and check if this array is symmetric. The tree is sym…

Problem Link: https://oj.leetcode.com/problems/binary-tree-level-order-traversal/ Traverse the tree level by level using BFS method. # Definition for a binary tree node # class TreeNode: # def __init__(self, x): # self.val = x # self.left = None # se…

Problem Link: https://oj.leetcode.com/problems/binary-tree-zigzag-level-order-traversal/ Just BFS from the root and for each level insert a list of values into the result. # Definition for a binary tree node # class TreeNode: # def __init__(self, x):…

Problem Link: https://oj.leetcode.com/problems/maximum-depth-of-binary-tree/ Simply BFS from root and count the number of levels. The code is as follows. # Definition for a binary tree node # class TreeNode: # def __init__(self, x): # self.val = x #…

Problem Link: https://oj.leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/ The basic idea is same to that for Construct Binary Tree from Inorder and Postorder Traversal. We solve it using a recursive function. First, we…

Problem Link: https://oj.leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/ This problem can be easily solved using recursive method. By given the inorder and postorder lists of the tree, i.e. inorder[1..n] and postorde…

Problem Link: https://oj.leetcode.com/problems/binary-tree-level-order-traversal-ii/ Use BFS from the tree root to traverse the tree level by level. The python code is as follows. # Definition for a binary tree node # class TreeNode: # def __init__(s…

Problem Link: http://oj.leetcode.com/problems/convert-sorted-array-to-binary-search-tree/ Same idea to Convert Sorted Array to Binary Search Tree, but we use a recursive function to construct the binary search tree. # Definition for a binary tree nod…

Problem Link: http://oj.leetcode.com/problems/convert-sorted-list-to-binary-search-tree/ We design a auxilar function that convert a linked list to a node with following properties: The node is the mid-node of the linked list. The node's left child i…

Problem Link: http://oj.leetcode.com/problems/minimum-depth-of-binary-tree/ To find the minimum depth, we BFS from the root and record the depth. For each level we add 1 to the depth and return the depth value when we reach a leaf. The python code is…

Problem Link: http://oj.leetcode.com/problems/path-sum-ii/ The basic idea here is same to that of Path Sum. However, since the problem is asking for all possible root-to-leaf paths, so we should use BFS but not DFS. The python code is as follows. # D…

Problem Link: http://oj.leetcode.com/problems/path-sum/ One solution is to BFS the tree from the root, and for each leaf we check if the path sum equals to the given sum value. The code is as follows. # Definition for a binary tree node # class TreeN…

Problem Link: http://oj.leetcode.com/problems/flatten-binary-tree-to-linked-list/ The problem is asking for flatterning a binary tree to linked list by the pre-order, therefore we could flatten tree from the root. For each node, we link it with its n…

Problem Link: http://oj.leetcode.com/problems/distinct-subsequences/ A classic problem using Dynamic Programming technique. Let m and n be the length of the strings T and S. Let R[i][j] be the count of distinct subsequence of T[0..i] in S[0..j]. Obvi…

Problem Link: http://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/ OK... Exactly same to Populating Next Right Pointers in Each Node.…