How to usethe Mathematical Approach (Summation of first N natural Numbers) in Javascript
The sum of the first N natural Numbers in a Range [1, N] is given by N * (N + 1) / 2.
To find the missing number, first find the sum of the first N natural number using the formula. And then use array traversal using a loop (for / while, …) and find the sum of array elements. At last, subtract the sum of array elements from the sum of natural numbers to find the missing element of an array.
Syntax:
missingElement = (N * (N + 1) / 1) - Sum of Array Elements
Example: The function findMissingNumber calculates the missing number in an array by finding the difference between the sum of the expected sequence and the sum of the array elements.
function findMissingNumber(arr) {
const n = arr.length + 1;
const sumOfFirstN = (n * (n + 1)) / 2;
let sumOfArray = 0;
for (let i = 0; i < n - 1; i++) {
sumOfArray = sumOfArray + arr[i];
}
let missingNumber = sumOfFirstN - sumOfArray;
return missingNumber;
}
const arr = [1, 2, 5, 4, 6, 8, 7];
const missingNumber = findMissingNumber(arr);
console.log("Missing Number: ", missingNumber);
Output
Missing Number: 3
JavaScript Program to Find the Missing Number
Given an array of size N-1 with integers in the range of [1, N]. The task is to find the missing number from the first N integers. There are no duplicate elements allowed in the array.
Examples:
Input : arr = [1, 2, 3, 5]
Output : 4
Input : arr = [1, 4, 3, 2, 6, 5, 7, 10, 9]
Output : 8
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