What is the most efficient way to identify the first duplicate number in an array that contains numbers ranging from 1 to the length of the array, ensuring that the second occurrence of the duplicate

Question

What is the most efficient way to identify the first duplicate number in an array that contains numbers ranging from 1 to the length of the array, ensuring that the second occurrence of the duplicate

Having some trouble with this code snippet. Tried running it but no luck. Here are the test cases:

Input: 2,1,3,5,3,2
Expected Output: 3;
Input: 2,4,3,5,1
Expected Output: -1
Input: 2,4,3,5,1,7

Check out the code below:

function FirstDuplicate(array) {
    var a = [5, 2, 3, 4, 2, 6, 7, 1, 2, 3];
    var firstDuplicate = "";
    for (var i = 0; i < a.length; i++) {
        for (var b = i + 1; b < a.length; b++) {
            if (a[i] === a[b])
                firstDuplicate = a.indexOf(a[i]);
            break;
        }
    }
    return firstDuplicate;
}

javascript arrays

Answer 1

Answer №1

To efficiently find the first duplicate in an array, you can utilize a Set. By creating an empty Set and continuously adding elements from the array to it, you can easily detect duplicates by checking if the element already exists in the Set. If a duplicate is found, simply return it.

function FindFirstDuplicate(array) {
    let passed = new Set();
    for(let num of array){
      if(passed.has(num)) return num;
      passed.add(num);
    }
    return -1;
}

console.log(FindFirstDuplicate([2,1,3,5,3,2]))
console.log(FindFirstDuplicate([2,4,3,5,1]))
console.log(FindFirstDuplicate([2,4,3,5,1,7]))

Answer 2

To efficiently find the first duplicate in an array, you can utilize a Set. By creating an empty Set and continuously adding elements from the array to it, you can easily detect duplicates by checking if the element already exists in the Set. If a duplicate is found, simply return it.

function FindFirstDuplicate(array) {
    let passed = new Set();
    for(let num of array){
      if(passed.has(num)) return num;
      passed.add(num);
    }
    return -1;
}

console.log(FindFirstDuplicate([2,1,3,5,3,2]))
console.log(FindFirstDuplicate([2,4,3,5,1]))
console.log(FindFirstDuplicate([2,4,3,5,1,7]))

Answer 3

Answer №2

To identify the first duplicate in an array, you can create a function that uses an object to keep track of values that have already been seen.

function findFirstDuplicate(array) {
   var seenValues = Object.create(null),
       index = 0,
       val;
   
   for (index = 0; index < array.length; index++) {
       val = array[index];
       if (seenValues[val]) return val;
       seenValues[val] = true;
   }
   return -1;
}

console.log(findFirstDuplicate([1, 7, 3, 5, 4, 2, 9, 3]));
console.log(findFirstDuplicate([1, 7, 3, 5, 4, 2, 9, 6]));

Answer 4

To identify the first duplicate in an array, you can create a function that uses an object to keep track of values that have already been seen.

function findFirstDuplicate(array) {
   var seenValues = Object.create(null),
       index = 0,
       val;
   
   for (index = 0; index < array.length; index++) {
       val = array[index];
       if (seenValues[val]) return val;
       seenValues[val] = true;
   }
   return -1;
}

console.log(findFirstDuplicate([1, 7, 3, 5, 4, 2, 9, 3]));
console.log(findFirstDuplicate([1, 7, 3, 5, 4, 2, 9, 6]));

Answer 5

Answer №3

By iterating over an array, we can push elements into an object. Once an element is encountered for the first time, it is labeled as true. If another true is found, we have identified the first duplicate in the array.

function findFirstDuplicate(arr) {
  let tmp = {};
  return (arr.find(v => (tmp[v] || (tmp[v] = true) && false)) || -1)
}

console.log(findFirstDuplicate([2,1,3,5,3,2]))
console.log(findFirstDuplicate([2,4,3,5,1]))
console.log(findFirstDuplicate([2,4,3,5,1,7]))

Answer 6

By iterating over an array, we can push elements into an object. Once an element is encountered for the first time, it is labeled as true. If another true is found, we have identified the first duplicate in the array.

function findFirstDuplicate(arr) {
  let tmp = {};
  return (arr.find(v => (tmp[v] || (tmp[v] = true) && false)) || -1)
}

console.log(findFirstDuplicate([2,1,3,5,3,2]))
console.log(findFirstDuplicate([2,4,3,5,1]))
console.log(findFirstDuplicate([2,4,3,5,1,7]))

What is the most efficient way to identify the first duplicate number in an array that contains numbers ranging from 1 to the length of the array, ensuring that the second occurrence of the duplicate

Answer №1

Answer №2

Answer №3

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