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Warm Up · Loops 02

Count Negative Numbers in an Array

Problem Statement

Write a function that returns the number of negative numbers in an array.

Example

Input: arr = [2, -6, 4, 8, 1, -9]

Process: -6 and -9 are below 0 → count = 2

Output: 2

Approach

  • Initialize a counter to 0.
  • Loop through the array.
  • If the element is less than 0, increment the counter.
  • Return the final count after the loop ends.

Time & Space Complexity

Time Complexity: O(n) - where n is the number of elements in the array.

Space Complexity: O(1) - only a counter variable is used.

Visualisation

1Start with the array[2, -6, 4, 8, 1, -9]
2Set the counterlet count = 0;
3For each element, is it negative?arr[i] < 0 ? count++
4Negative count2

Explanation

  • count starts at 0 and only goes up when a negative number is found.
  • arr[i] < 0 is true for -6 and -9, so count becomes 2.
  • The function returns count instead of printing it, so the caller decides what to do with it.

Your solution

Solve it in JavaScript and print the answer with console.log(). Run to see your output, then Submit to check it against the test cases.

// Write your solution in JavaScript
// Print the answer with console.log()
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Write your own solution and press Submit once to unlock the answer.

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