【Video】Give me 3 minutes - How we think about a solution
Intuition\nWe use subtraction.\n\n---\n\n# Solution Video\n\nhttps://youtu.be/tjILACCjQI0\n\n\u25A0 Timeline of the video\n\n0:04 Explain how we can solve this 
# Intuition\nWe use subtraction.\n\n---\n\n# Solution Video\n\nhttps://youtu.be/tjILACCjQI0\n\n\u25A0 Timeline of the video\n\n`0:04` Explain how we can solve this question\n`1:29` Coding\n`2:40` Time Complexity and Space Complexity\n`3:13` Step by step algorithm of my solution code\n\n### \u2B50\uFE0F\u2B50\uFE0F Don\'t forget to subscribe to my channel! \u2B50\uFE0F\u2B50\uFE0F\n\n**\u25A0 Subscribe URL**\nhttp://www.youtube.com/channel/UC9RMNwYTL3SXCP6ShLWVFww?sub_confirmation=1\n\nSubscribers: 3,469\nMy first goal is 10,000 (It\'s far from done \uD83D\uDE05)\nThank you for your support!\n\n---\n\n# Approach\n\n## How we think about a solution\n\nWe know that we have the same number of start cities and end cities. I thought if I create group of start cities and end cities, we can use subtraction.\n\n```\nInput: paths = [["B","C"],["D","B"],["C","A"]]\n```\n\nWe use `set` to create groups because we can use subtraction with set easily. Start group and end group should be\n```\nstart_cities = {"B", "D", "C"}\n```\n```\nend_cities = {"C", "B", "A"}\n```\nThen subtract `end` - `start`, which means remove `common cities` in the end group.\n\n```\nend_cities - start_cities\n= {"C", "B", "A"} - {"B", "D", "C"}\n```\nWe have "C" and "B" in both groups, so in the end, end group should be\n```\ndestination = {"A"}\n```\nThen just pop from `set`\n```\nOutput: "A"\n```\nThere is not "A" city in start group, so we are sure that "A" is definitely destination city.\n\nEasy! \uD83D\uDE04\nLet\'s see a real algorithm!\n\nI usually write 4 languages Python, JavaScript, Java and C++. But today, I don\'t have enough time. I want to create a video before I go out. \n\nIf possible, could someone convert this Python code to JavaScript, Java, and C++?\n\n\n---\n\n# Complexity\n- Time complexity: $$O(n)$$\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity: $$O(n)$$\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n```python []\nclass Solution:\n    def destCity(self, paths: List[List[str]]) -> str:\n        start_cities, end_cities = map(set, zip(*paths))\n        destination = (end_cities - start_cities).pop()\n        return destination\n```\n\n## Step by step algorithm\n\n1. **Create Sets for Start and End Cities:**\n   - Use `zip(*paths)` to transpose the matrix of paths, separating the start cities and end cities.\n   - Apply `set` to convert each set of cities to unique sets.\n\n    ```python\n    start_cities, end_cities = map(set, zip(*paths))\n    ```\n\n2. **Find the Destination City:**\n   - Use set subtraction (`end_cities - start_cities`) to find the set of cities that are destinations but not starting points.\n   - Use `pop()` to retrieve any element from the set (since we expect only one element).\n\n    ```python\n    destination = (end_cities - start_cities).pop()\n    ```\n\n3. **Return the Result:**\n   - Return the found destination city.\n\n    ```python\n    return destination\n    ```\n\nThis code essentially finds the city that is a destination but not a starting point by utilizing sets and set operations. The order of the paths and the uniqueness of cities in sets make it efficient for this specific task.\n\n---\n\nThank you for reading my post.\n\u2B50\uFE0F Please upvote it and don\'t forget to subscribe to my channel!\n\n\u25A0 Subscribe URL\nhttp://www.youtube.com/channel/UC9RMNwYTL3SXCP6ShLWVFww?sub_confirmation=1\n\n\u25A0 Twitter\nhttps://twitter.com/CodingNinjaAZ\n\n### My next daily coding challenge post and video.\n\npost\nhttps://leetcode.com/problems/valid-anagram/solutions/4410317/video-give-me-5-minutes-4-solutions-how-we-think-about-a-solution/\n\nvideo\nhttps://youtu.be/UR9geRGBvhk\n\n\u25A0 Timeline of the video\n\n`0:03` Explain Solution 1\n`2:52` Coding of Solution 1\n`4:38` Time Complexity and Space Complexity of Solution 1\n`5:04` Step by step algorithm of my solution code of Solution 1\n`5:11` Explain Solution 2\n`8:20` Coding of Solution 2\n`10:10` Time Complexity and Space Complexity of Solution 2\n`10:21` Step by step algorithm of my solution code of Solution 2\n`10:38` Coding of Solution 3\n`12:18` Time Complexity and Space Complexity of Solution 3\n`13:15` Coding of Solution 4\n`13:37` Time Complexity and Space Complexity of Solution 4\n`13:52` Step by step algorithm of my solution code of Solution 3\n\n### My previous daily coding challenge post and video.\n\npost\nhttps://leetcode.com/problems/difference-between-ones-and-zeros-in-row-and-column/solutions/4401811/video-give-me-5-minutes-how-we-think-about-a-solution/\n\nvideo\nhttps://youtu.be/swafoNFu99o\n\n\u25A0 Timeline of the video\n\n`0:06` Create number of 1 in each row and column\n`1:16` How to calculate numbers at each position \n`4:03` Coding\n`6:32` Time Complexity and Space Complexity\n`7:02` Explain zip(*grid)\n`8:15` Step by step algorithm of my solution code\n\n
['Array', 'Hash Table', 'String', 'Python3']