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Recursion for Coding Interviews in JavaScript

Solution Review: Search the First Occurrence of a Number

Explore how to locate the first occurrence of a number within an array by comparing iterative and recursive approaches. Understand base and recursive cases, walk through examples, and learn to implement both solutions effectively.

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Solution #1: Iterative Method

Javascript (babel-node)
function firstIndex(arr, testVariable, currentIndex) { // returns the first occurrence of testVariable
  
  while (currentIndex < arr.length) { // Iterate over the array
    if (arr[currentIndex] == testVariable) {  // Return the current index if testVariable found
      return currentIndex;
    } 
    currentIndex += 1;
  }
  return -1;
}
// Driver Code
var arr = [9, 8, 1, 8, 1, 7];
var testVariable = 1;
var currentIndex = 0;
console.log(firstIndex(arr, testVariable, currentIndex));

Explanation

To find the first occurrence of testVariable we iterate over the entire array and return the currentIndex when testVariable is found. Let’s look at an illustration:

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