Leetcode Problem 1915. Number of Wonderful Substrings

1915. Number of Wonderful Substrings

Leetcode Solutions

Bitmask and Prefix Sum Approach

  1. Initialize a prefix sum array count with size 1024 (2^10) and set count[0] to 1 to represent the empty substring.
  2. Initialize a variable mask to 0 to represent the current state of the bitmask.
  3. Initialize a variable res to 0 to store the total count of wonderful substrings.
  4. Iterate through each character c in the input string word: a. Update the mask by toggling the bit corresponding to the character c. b. Add count[mask] to res because a previous state with the same bitmask indicates a substring with all even counts. c. For each bit position from 0 to 9, toggle the bit in mask and add count[mask ^ (1 << bit)] to res to account for substrings with exactly one odd character count. d. Increment count[mask] to include the current state in the prefix sum array.
  5. Return the total count res.
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Brute Force Approach

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