Accumulate Count

The accumulate count involves counting the number of elements that satisfy a certain condition in a range of an array. This is similar to range sum, except instead of summing values, we count elements meeting some criteria.

Some example code:

Java:

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// Count even elements in range [i, j]
int accumulateCount(int[] nums, int i, int j) {
  int count = 0;
  for (int k = i; k <= j; k++) {
    if (nums[k] % 2 == 0) {
      count++; 
    }
  }
  return count;
}

int[] nums = {1, 2, 4, 5, 6};
int evenCount = accumulateCount(nums, 1, 3); // Returns 2

C++:

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// Count positive elements in range [i, j]
int accumulateCount(vector<int>& nums, int i, int j) {
  int count = 0;
  for (int k = i; k <= j; k++) {
    if (nums[k] > 0) {
      count++;
    }
  }
  return count; 
}

vector<int> nums{1, -2, 4, 5, -6};
int posCount = accumulateCount(nums, 1, 4); // Returns 3

Python:

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# Count odd elements in range [i, j]  
def accumulate_count(nums, i, j):
  count = 0
  for k in range(i, j+1):
    if nums[k] % 2 == 1:
      count += 1
  return count
      
nums = [1, 2, 3, 4, 5]  
oddCount = accumulate_count(nums, 1, 3) # Returns 2

The key steps are:

1. Initialize a count variable
2. Iterate through the range, incrementing count if element meets criteria
3. Return the total count

This allows counting elements satisfying any condition in a range of an array.

Accumulate Count is the concept of counting the occurrences of elements as you traverse a list or array. This technique is often applied in problems that require determining the frequency of elements, such as identifying the most common element or finding out if an element appears more than a certain number of times. It involves maintaining a running tally of each unique element encountered.

Solution

Java

You can use a HashMap to keep track of the counts for each unique element.

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public Map<Integer, Integer> accumulateCount(int[] nums) {
    Map<Integer, Integer> countMap = new HashMap<>();
    for (int num : nums) {
        countMap.put(num, countMap.getOrDefault(num, 0) + 1);
    }
    return countMap;
}

C++

In C++, you can use an unordered_map to achieve the same result.

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#include <unordered_map>
#include <vector>

std::unordered_map<int, int> accumulateCount(std::vector<int>& nums) {
    std::unordered_map<int, int> countMap;
    for (int num : nums) {
        countMap[num]++;
    }
    return countMap;
}

Python

In Python, a Counter from the collections library is a convenient way to count occurrences.

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from collections import Counter

def accumulate_count(nums):
    return Counter(nums)

These code snippets iterate through the given array, counting the occurrences of each unique element and storing the counts in a map or dictionary. This structure allows for efficient querying of the count of any given element, thereby facilitating various statistical and frequency-based analyses.

Tabular Representation

Below is a table that demonstrates the process of accumulating counts for an array. Let’s assume our input array is [4, 2, 4, 3, 2].

Here’s a step-by-step explanation:

• In the first iteration, the element 4 is encountered for the first time, so its count is initialized to 1.
• In the second iteration, the element 2 is encountered for the first time, so its count is initialized to 1.
• In the third iteration, the element 4 is encountered again, so its count is incremented to 2.
• In the fourth iteration, the element 3 is encountered for the first time, so its count is initialized to 1.
• In the fifth and final iteration, the element 2 is encountered again, so its count is incremented to 2.

This table illustrates how the accumulate count algorithm iteratively builds up the counts for each unique element in the input array.