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Posts tagged as “path”

花花酱 LeetCode 576. Out of Boundary Paths

Problem

There is an m by n grid with a ball. Given the start coordinate (i,j) of the ball, you can move the ball to adjacent cell or cross the grid boundary in four directions (up, down, left, right). However, you can at most move N times. Find out the number of paths to move the ball out of grid boundary. The answer may be very large, return it after mod 109 + 7.

Example 1:

Input:m = 2, n = 2, N = 2, i = 0, j = 0
Output: 6
Explanation:

Example 2:

Input:m = 1, n = 3, N = 3, i = 0, j = 1
Output: 12
Explanation:

Note:

  1. Once you move the ball out of boundary, you cannot move it back.
  2. The length and height of the grid is in range [1,50].
  3. N is in range [0,50].

Solution

Time complexity: O(m*n + N * m * n)

Space complexity: O(N*m*n) -> O(m*n)

C++

Recursion with memorization

no loops

 

Related Problems

花花酱 LeetCode 329. Longest Increasing Path in a Matrix

Problem

Given an integer matrix, find the length of the longest increasing path.

From each cell, you can either move to four directions: left, right, up or down. You may NOT move diagonally or move outside of the boundary (i.e. wrap-around is not allowed).

Example 1:

Input: nums = 
[
  [9,9,4],
  [6,6,8],
  [2,1,1]
] 
Output: 4 
Explanation: The longest increasing path is [1, 2, 6, 9].

Example 2:

Input: nums = 
[
  [3,4,5],
  [3,2,6],
  [2,2,1]
] 
Output: 4 
Explanation: The longest increasing path is [3, 4, 5, 6]. Moving diagonally is not allowed.

Solution1: DFS + Memorization

Time complexity: O(mn)

Space complexity: O(mn)

C++

Solution2: DP

DP

Time complexity: O(mn*log(mn))

Space complexity: O(mn)

 

花花酱 LeetCode 609. Find Duplicate File in System

Problem

https://leetcode.com/problems/find-duplicate-file-in-system/description/

题目大意:输出系统中文件内容相同的文件名。

Given a list of directory info including directory path, and all the files with contents in this directory, you need to find out all the groups of duplicate files in the file system in terms of their paths.

A group of duplicate files consists of at least two files that have exactly the same content.

A single directory info string in the input list has the following format:

"root/d1/d2/.../dm f1.txt(f1_content) f2.txt(f2_content) ... fn.txt(fn_content)"

It means there are n files (f1.txtf2.txt … fn.txt with content f1_contentf2_content … fn_content, respectively) in directory root/d1/d2/.../dm. Note that n >= 1 and m >= 0. If m = 0, it means the directory is just the root directory.

The output is a list of group of duplicate file paths. For each group, it contains all the file paths of the files that have the same content. A file path is a string that has the following format:

"directory_path/file_name.txt"

Example 1:

Input:
["root/a 1.txt(abcd) 2.txt(efgh)", "root/c 3.txt(abcd)", "root/c/d 4.txt(efgh)", "root 4.txt(efgh)"]
Output:  
[["root/a/2.txt","root/c/d/4.txt","root/4.txt"],["root/a/1.txt","root/c/3.txt"]]

Note:

  1. No order is required for the final output.
  2. You may assume the directory name, file name and file content only has letters and digits, and the length of file content is in the range of [1,50].
  3. The number of files given is in the range of [1,20000].
  4. You may assume no files or directories share the same name in the same directory.
  5. You may assume each given directory info represents a unique directory. Directory path and file info are separated by a single blank space.

Follow-up beyond contest:

  1. Imagine you are given a real file system, how will you search files? DFS or BFS?
  2. If the file content is very large (GB level), how will you modify your solution?
  3. If you can only read the file by 1kb each time, how will you modify your solution?
  4. What is the time complexity of your modified solution? What is the most time-consuming part and memory consuming part of it? How to optimize?
  5. How to make sure the duplicated files you find are not false positive?

Solution: HashTable

Key: content, Value: Array of filenames

Time complexity: O(n)

Space complexity: O(n)

C++

 

花花酱 LeetCode 687. Longest Univalue Path

题目大意:给你一棵二叉树,返回一条最长的路径,要求路径上所有的节点值都相同。

https://leetcode.com/problems/longest-univalue-path/description/

Problem: 

Given a binary tree, find the length of the longest path where each node in the path has the same value. This path may or may not pass through the root.

Note: The length of path between two nodes is represented by the number of edges between them.

Example 1:

Input:

              5
             / \
            4   5
           / \   \
          1   1   5

Output:

2

Example 2:

Input:

              1
             / \
            4   5
           / \   \
          4   4   5

Output:

2

Note: The given binary tree has not more than 10000 nodes. The height of the tree is not more than 1000.



Idea:

DFS

Solution: Recursion

Time complexity: O(n)

Space complexity: O(n)

C++

Java

Python3

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