Most Frequent Number Following Key In an Array

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from typing import List

class Solution:
    def mostFrequent(self, nums: List[int], key: int) -> int:
        cnt = [0]*1001
        res = 0
        for i in range(1, len(nums)):
            if nums[i - 1] == key:
                cnt[nums[i]] += 1
                if cnt[nums[i]] > cnt[res]:
                    res = nums[i]
        return res

In this code:

1. cnt is initialized as a list of zeros with a length of 1001, which corresponds to the integer array in the C++ code.
2. res corresponds to the result variable in the C++ code and is initialized as 0.
3. The for loop iterates from 1 to the length of nums, corresponding to the C++ code.
4. If the previous element of nums is equal to the key, the count of the current element in cnt is incremented.
5. If the incremented count is larger than the count of the current result, the result is updated to the current number. This corresponds to the condition inside the if statement in the C++ code.
6. The result is then returned.

Q&A

Kindly help with my code….idk where it’s going wrong

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int mostFrequent(vector & nums, int key) {
  int idx = -1, cnt = 1;
  for (int i = 0; i < nums.size(); i++) {
    if (nums[i] == key) {
      idx = i + 1;
      break;
    }
  }
  for (int i = idx; i < nums.size() - 1; i++) {
    if (nums[i] != key) continue;
    if (nums[i + 1] == nums[idx]) cnt++;
    else cnt--;
    if (cnt == 0) {
      idx = i + 1;
      cnt++;
    }
  }
  return nums[idx];
}

The original code tries to find the most frequent number that follows the key number in the nums array. However, it seems to have a logical error. Once the key is found in the array, the code checks the next number (if it exists), but the subsequent loop does not seem to be working as intended.

In your code, you are incrementing the count cnt when you find a number that equals nums[idx] but this logic will not work correctly. The variable idx was only set at the beginning and it does not update after the first iteration. Therefore, you are not correctly counting the occurrences of the number that follows key in the nums array.

Also, you are decrementing the count cnt when you find a number that is not equal to nums[idx] and resetting the idx when the count cnt reaches zero. This is not correct because you are trying to count the number that occurs most frequently after key, not just the subsequent number.

Here is a corrected version of your code:

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int mostFrequent(vector<int>& nums, int key) {
    unordered_map<int, int> count;
    int maxCount = 0, res = -1;

    for (int i = 0; i < nums.size() - 1; ++i) {
        if (nums[i] == key) {
            ++count[nums[i + 1]];
            if (count[nums[i + 1]] > maxCount) {
                maxCount = count[nums[i + 1]];
                res = nums[i + 1];
            }
        }
    }
    return res;
}

In this version of the function, an unordered_map count is used to keep track of the count of each number that follows key in the nums array. The maxCount variable is used to store the maximum count encountered so far, and res stores the number that has the maximum count. The for loop iterates over the nums array, and if the current number equals key, it increments the count of the next number in the count map. If this new count is greater than the maxCount, maxCount and res are updated. At the end of the function, res is returned, which is the most frequently occurring number after key in the nums array.