How to find the missing number in an int array of 1 to 100 in JS
Overview
Consider an array of numbers from 1 to 100. In this array, duplicate elements are not allowed. Also, there is one number missing in this array. We will find that by following the steps provided below:
Step 1: Calculate the sum of numbers from 1 to 100 using the sum of natural numbers formula given below:
Step 2: Find the sum of the values present in the array.
Step 3: Subtract the sum of the elements of the array from the sum of 1 to 100 numbers. We'll get the missing number as a result.
Example
function findMissedNum(arrayOfNumbers, n = 100) {if(arrayOfNumbers.length === n) {console.log("no number is missed");}if(arrayOfNumbers.length < (n - 1) ) {console.log("more than one number is missed")}let totalSum = (n * (n+1)) / 2;let sumOfArray = 0;for(let i of arrayOfNumbers){sumOfArray += i;}return totalSum - sumOfArray;}// create an array with values 0 to 100let arrayOfNumbers = Array.from( Array(101).keys())// remove the 0th elementarrayOfNumbers.shift();// now the array will 1 to 100// remove the value at index 50.(means remove 51 from the array)arrayOfNumbers.splice(50, 1)// now the array is 1 to 100 but without the number 51let missedNum = findMissedNum(arrayOfNumbers, 100);console.log("The missing number is :", missedNum)
Explanation
- Lines 1–16: We create a
findMissedNumfunction that will find the missing number of an array using the above algorithm.
- Line 18: We create a new array,
arrayOfNumbers.
- The
Array(101)array returns an array with 101 empty elements.
- On the created array, we call the
keysmethod, which returns an array iterator object that contains the key of each index. In our case, iterator from is from 0 to 100. - We use the
Array.frommethod with the array iterator as an argument. This method returns a new array with the values of the array iterator. We get an array with values 0 to 100.
- Line 21: We use the
shiftmethod to remove the first element of the array. Now the array will be 1 to 100.
- Line 26: We use the
slicemethod to remove the element at index 50. Element 51 will be removed from the array.
- Line 30: We call the
findMissedNummethod. This method returns the missing number 51 as result.
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