Let Code Day89 "62. Unique Paths" Starting from Zero

Overview

It seems that coding tests are conducted overseas in interviews with engineers, and in many cases, the main thing is to implement specific functions and classes according to the theme.

Apparently, many engineers take measures on the site called LetCode.

It is a site that trains the algorithmic power that can withstand the coding test that is being done in the early story, and it is an inevitable path for those who want to build a career at an overseas tech company.

I wrote it in a big way, but I have no plans to have such an interview at the moment.

However, as an IT engineer, it would be better to have the same level of algorithm power as a person, so I would like to solve the problem irregularly and write down the method I thought at that time as a memo.

Leetcode

I'm solving it with Python3.

Leet Code Table of Contents Starting from Zero

Last time Leet Code Day 88 "139. Word Break" starting from zero

Twitter I'm doing it.

** Technical Blog Started! !! ** ** I think the technology will write about LetCode, Django, Nuxt, and so on. ** This is faster to update **, so please bookmark it!

problem

62. Unique Paths The difficulty level is Medium. This is an excerpt from Leet Code 60 Questions I Want to Solve for Coding Interview Preparation.

The problem is finding the number of unique routes. The robot is located in the upper left corner of the m x n grid (it is labeled" Start "in the figure below).

Note that the robot can only move down or to the right at any given time. The robot is about to reach the lower right corner of the grid (it is labeled "Finish" in the figure below).

I will not post a figure this time, so if you want to chew and think about it, please check directly with the link in question.

Example 1:

Input: m = 3, n = 2 Output: 3 Explanation: From the top-left corner, there are a total of 3 ways to reach the bottom-right corner:

  1. Right -> Right -> Down
  2. Right -> Down -> Right
  3. Down -> Right -> Right

Example 2:

Input: m = 7, n = 3 Output: 28

solution

It's a matter of finding the number of unique routes. This is also a very effective type of problem to solve with Dynamic Programming as before.

By the way, regarding how to find the route, here explains in English in a super easy-to-understand manner. I think it's relatively easy to understand even for those who are not very familiar with it, so I recommend you to take a look when solving such a problem for the first time.

Then the answer.

class Solution:
    def uniquePaths(self, m: int, n: int) -> int:
        if m == 1 or n == 1:
            return 1
        if n < m:
            self.uniquePaths(n,m)
        dp = [1]*n
        for i in range(1,m):
            for j in range(1,n):
                dp[j] += dp[j-1]
        return dp[-1]
# Runtime: 28 ms, faster than 84.67% of Python3 online submissions for Unique Paths.
# Memory Usage: 13.8 MB, less than 74.12% of Python3 online submissions for Unique Paths.

In addition, in the first half

dp = [1]*n

The answer will pass even if you do not have the above code. However, it is safer to write it because exceptions may occur. In fact, many people write in the answer of discuss, and I think that if it is a coding interview etc., it may be rushed.

After that, the code after that is basically the same as the code explained in the video introduced earlier, so it seems that explanation is not necessary so much.

By the way, if you search for this problem on YouTube, it is introduced that you have been asked on Amazon, so if you are interested, you may want to check it.

So that's it for this time. Thank you for your hard work.

Recommended Posts

Let Code Day89 "62. Unique Paths" Starting from Zero
Let Code Day58 Starting from Zero "20. Valid Parentheses"
Let Code Day16 Starting from Zero "344. Reverse String"
Let Code Day49 starting from zero "1323. Maximum 69 Number"
Let Code Day 55 "22. Generate Parentheses" Starting from Zero
Let Code Day18 starting from zero "53. Maximum Subarray"
Let Code Day 13 "338. Counting Bits" Starting from Zero
Let Code Day71 Starting from Zero "1496. Path Crossing"
Let Code Day 61 "7. Reverse Integer" starting from zero
Let Code Day 82 "392. Is Subsequence" Starting from Zero
Let Code Day51 Starting from Zero "647. Palindromic Substrings"
Let Code Day 50 "739. Daily Temperatures" Starting from Zero
Let Code Day 15 "283. Move Zeroes" starting from zero
Let Code Day14 starting from zero "136. Single Number"
Let Code Day 43 "5. Longest Palindromic Substring" Starting from Zero
Let Code Day74 starting from zero "12. Integer to Roman"
Let Code Day 42 "2. Add Two Numbers" Starting from Zero
Let Code Day57 Starting from Zero "35. Search Insert Position"
Let Code Day47 Starting from Zero "14. Longest Common Prefix"
Let Code Day78 Starting from Zero "206. Reverse Linked List"
Let Code Day75 starting from scratch "15.3 Sum"
Let Code Day 44 "543. Diameter of Binary Tree" starting from zero
Let Code Day 64 starting from zero "287. Find the Duplicate Number"
Let Code Day 84 starting from zero "142. Linked List Cycle II"
Let Code Day 29 "46. Permutations" starting from scratch
Let Code Day24 Starting from Zero "21. Merge Two Sorted Lists"
Let Code Day12 Starting from Zero "617. Merge Two Binary Trees"
Let Code Day2 Starting from Zero "1108. Defanging an IP Address"
Let Code Day70 Starting from Zero "295. Find Median from Data Stream"
Let Code Day81 "347. Top K Frequent Elements" Starting from Zero
Let Code Day48 Starting from Zero "26. Remove Duplicates from Sorted Array"
Let Code Day87 Starting from Zero "1512. Number of Good Pairs"
Let Code Day 60 starting from zero "1481. Least Number of Unique Integers after K Removals"
Let Code Day67 Starting from Zero "1486. XOR Operation in an Array"
Let Code Day56 Starting from Zero "5453. Running Sum of 1d Array"
Let Code Day7 starting from zero "104. Maximum Depth of Binary Tree"
Let Code Day86 Starting from Zero "33. Search in Rotated Sorted Array"
Let Code Day92 Starting from Zero "4. Median of Two Sorted Arrays"
Let Code Day5 starting from zero "1266. Minimum Time Visiting All Points"
Let Code Day 35 "160. Intersection of Two Linked Lists" Starting from Zero
Let Code Day83 Starting from Zero "102. Binary Tree Level Order Traversal"
Let Code Day 27 "101. Symmetric Tree" starting from scratch
Let Code Day 41 "394. Decode String" starting from scratch
Let Code Day 25 "70. Climbing Stairs" starting from scratch
Let Code Table of Contents Starting from Zero
Let Code Day69 starting from scratch "279. Perfect Squares"
Let Code Day 34 starting from scratch "118. Pascal's Triangle"
Let Code Day85 starting from scratch "6. ZigZag Conversion"
Let Code Day20 starting from scratch "134. Gas Station"
Let Code Day 88 "139. Word Break" starting from scratch
Let Code Day 28 "198. House Robber" starting from scratch
Let Code Day 39 "494. Target Sum" starting from scratch
Let Code Day 36 "155. Min Stack" starting from scratch
Let Code Day 17 "169. Majority Element" starting from scratch
Let Code Day 33 "1. Two Sum" starting from scratch
Let Code Day 40 Starting from Zero "114. Flatten Binary Tree to Linked List"
Let Code Day 91 "153. Find Minimum in Rotated Sorted Array" starting from zero
Let Code Day59 starting from zero "1221. Split a String in Balanced Strings"
Let Code Day 11 Starting from Zero "1315. Sum of Nodes with Even-Valued Grandparent"
Let Code Day6 Starting from Zero "1342. Number of Steps to Reduce a Number to Zero"
Let Code Day 23 "226. Invert Binary Tree" starting from scratch