Leetcode Problem 2826. Sorting Three Groups

2826. Sorting Three Groups

Leetcode Solutions

Dynamic Programming with Memoization

  1. Define a recursive function dfs(i, prev) that returns the minimum number of operations needed starting from index i with the previous group number prev.
  2. If i is equal to the length of nums, return 0 as we have processed all elements.
  3. If the result for the current state (i, prev) is already computed, return it from the memoization table.
  4. If nums[i] is equal to prev, recursively call dfs(i+1, prev) as no operation is needed.
  5. If nums[i] is less than prev, recursively call dfs(i+1, prev) and add 1 to the result as we need to perform an operation.
  6. If nums[i] is greater than prev, we have two choices: leave it as is or change it to prev. Compute the minimum of dfs(i+1, nums[i]) and dfs(i+1, prev) + 1.
  7. Store the result in the memoization table before returning it.
  8. Initialize the memoization table and call dfs(0, 1) to get the final result.
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Prefix Sum with Brute Force

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