C++ | MAP |
Intuition\n Describe your first thoughts on how to solve this problem. Upon reviewing the code, it appears that the SnapshotArray class is designed to create an
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->Upon reviewing the code, it appears that the `SnapshotArray` class is designed to create an array-like structure that supports snapshots of its elements. Each element can be set using the `set` function, and snapshots can be taken using the `snap` function. The `get` function allows retrieving the value of an element at a specific index and snapshot ID.\n\nTo solve this problem, I would consider implementing the following steps:\n\n1. Initialize the `v` vector: In the constructor `SnapshotArray`, create a vector `v` of length `length` and initialize each element as an empty map. This will represent the array and its snapshots.\n\n2. Setting element values: The `set` function takes an index and a value as input. Use the index to access the corresponding map in `v` and set the value at the current snapshot ID (`s`). This can be done by assigning `v[index][s] = val`.\n\n3. Taking snapshots: The `snap` function increments the `s` counter and returns the current snapshot ID (`s-1`).\n\n4. Retrieving element values: The `get` function takes an index and a snapshot ID as input. First, check if the map at the given index contains the snapshot ID. If it does not, find the closest snapshot ID using `lower_bound`. Subtract 1 from the iterator to get the previous snapshot ID and access the corresponding value.\n\n5. Analyzing time and space complexity: Evaluate the time and space complexity of the code to understand its efficiency.\n\nOverall, the steps involve initializing the data structure, setting values, taking snapshots, and retrieving values based on the given index and snapshot ID.\n\n# Approach\n<!-- Describe your first thoughts on how to solve this problem. -->Upon analyzing the code, it seems that the `SnapshotArray` class aims to provide a data structure that supports setting and retrieving values at different indices, as well as taking snapshots of the array\'s state at any given point. \n\nTo solve this problem, I would approach it by utilizing a combination of data structures and algorithms. Here\'s a step-by-step plan based on my initial thoughts:\n\n1. Data structure: The core data structure to store the array and its snapshots could be a vector of maps. Each element of the vector would represent an index, and the associated map would store the values at different snapshot IDs. This structure allows efficient retrieval of values at specific indices and snapshot IDs.\n\n2. Initialization: In the constructor `SnapshotArray(int length)`, create a vector of size `length`. Iterate over the vector and initialize each element as an empty map. This ensures that each index in the array is represented, and initially, all values are set to 0.\n\n3. Setting values: The `set` function takes an index and a value as input. Access the map at the given index and set the value at the current snapshot ID (`s`). If the map doesn\'t have an entry for the current snapshot ID, create one and assign the value. This approach ensures that only the relevant snapshots have their values stored.\n\n4. Taking snapshots: The `snap` function increments the `s` counter and returns the current snapshot ID. Simply increment `s` by 1, which represents the total number of snapshots taken so far, and return `s-1`.\n\n5. Retrieving values: The `get` function takes an index and a snapshot ID as input. Check if the map at the given index has an entry for the specified snapshot ID. If it does, return the value directly. If not, use `lower_bound` to find the iterator pointing to the closest snapshot ID that is less than or equal to the given ID. Subtract 1 from the iterator to obtain the previous snapshot ID and retrieve the value associated with it.\n\n6. Analyzing complexity: Evaluate the time and space complexity of the code to determine its efficiency and potential for optimization.\n\nBy following this plan, we can effectively implement the functionality provided by the `SnapshotArray` class, allowing for efficient setting, retrieving, and snapshotting of array values.\n\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ --> O(1)\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ --> O(n)\n\n# Code\n```\nclass SnapshotArray {\npublic:vector<map<int,int>>v;\nint s=0;\n    SnapshotArray(int length)\n     {\n        v.resize(length);\n        for(int i=0;i<length;i++)\n        {\n            v[i][0]=0;\n        }\n    }\n    void set(int index, int val)\n     {\n        v[index][s]=val;\n    }   \n    int snap()\n     {\n        s++;\n       return s-1;\n    }   \n    int get(int index, int snap_id) \n    {\n        if(v[index].find(snap_id)==v[index].end())\n        {\n            auto it= --v[index].lower_bound(snap_id);\n            return it->second;\n        }\n        return v[index][snap_id];\n    }\n};\n\n//Must Upvote\n```
['Array', 'Hash Table', 'Binary Search', 'Ordered Map', 'C++']