beehard

摘要： Follow up for "Unique Paths": Now consider if some obstacles are added to the grids. How many unique paths would there be? An obstacle and empty space is marked as 1 and 0 respectively in the grid. For example, There is one obstacle in the middle of a 3x3 grid as illustrated below. [ [0,0, 阅读全文

摘要： Given n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the histogram. For example, Given height = [2,1,5,6,2,3], return 10. Solution: 1. Only calucate area when reaching local maximum value. 2. Keep a n... 阅读全文

摘要： Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules (http://sudoku.com.au/TheRules.aspx). The Sudoku board could be partially filled, where empty cells are filled with the character '.'. Solution: 1. Traverse the Sudoku only once. 2. Bit manipulation. Use only one bit .. 阅读全文

摘要： Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place. Follow up: Did you use extra space? A straight forward solution using O(mn) space is probably a bad idea. A simple improvement uses O(m + n) space, but still not the best solution. Could you devise a consta 阅读全文

摘要： A robot is located at the top-left corner of a m x n grid. The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below). How many possible unique paths are there? Solution: 1. Use fo 阅读全文

摘要： Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root). For example: Given binary tree {3,9,20,#,#,15,7}, 3 / \ 9 20 / \ 15 7 return its bottom-up level order traversal as: [ [15,7] [9,20], ... 阅读全文

摘要： Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level). For example: Given binary tree {3,9,20,#,#,15,7}, 3 / \ 9 20 / \ 15 7 return its level order traversal as: [ [3], [9,20], [15,7] ] Solution: 1. Use queue. I... 阅读全文

摘要： Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum. For example: Given the below binary tree and sum = 22, 5 / \ 4 8 / / \11 13 4 / \ / \7 2 5 1 return [ [5,4,11,2], [5,8,4,5] ] Solution: DFS. 1 /** 2 * Defini... 阅读全文

摘要： Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum. For example: Given the below binary tree and sum = 22, 5 / \ 4 8 / / \11 13 4/ \ \ 7... 阅读全文

摘要： Given a binary tree, determine if it is a valid binary search tree (BST). Assume a BST is defined as follows: The left subtree of a node contains only nodes with keys less than the node's key. The right subtree of a node contains only nodes with keys greater than the node's key. Both the lef 阅读全文