Arrays - Find missing numbers in a Sequence

Question

I\'m trying to find an easy way to loop (iterate) over an array to find all the missing numbers in a sequence, the array will look a bit like the one below.

var nu

Answer 1

ES6-Style

var arr = [0189459, 0189460, 0189461, 0189463, 0189465]; 
var [min,max] = [Math.min(...arr), Math.max(...arr)];
var out = Array.from(Array(max-min),(v,i)=>i+min).filter(i=>!arr.includes(i));

Result: [189462, 189464]

Answer 2

Assuming that there are no duplicates

let numberArray = [];

for (let i = 1; i <= 100; i++) {
  numberArray.push(i);
}
let deletedArray = numberArray.splice(30, 1);
let sortedArray = numberArray.sort((a, b) => a - b);
let array = sortedArray;

function findMissingNumber(arr, sizeOfArray) {
  total = (sizeOfArray * (sizeOfArray + 1)) / 2;
  console.log(total);
  for (i = 0; i < arr.length; i++) {
    total -= arr[i];
  }
  return total;
}

console.log(findMissingNumber(array, 100));

Answer 3

This can now be done easily as a one-liner with the find method:

const arr = [1,2,3,5,6,7,8,9];

return arr.find((x,i) => arr[i+1]-x > 1) + 1

//4

Answer 4

const findMissing = (numarr) => {
  for(let i = 1; i <= numarr.length; i++) {
      if(i - numarr[i-1] !== 0) {
        console.log('found it', i)
        break;
      } else if(i === numarr.length) console.log('found it', numarr.length + 1)
    }
  };

console.log(findMissing([1,2,3,4,5,6,7,8,9,10,11,12,13,14]))

Answer 5

To find a missing number in a sequence, First of all, We need to sort an array. Then we can identify what number is missing. I am providing here full code with some test scenarios. this code will identify only missing positive number, if you pass negative values even then it gives positive number.

function findMissingNumber(inputAr) {
  // Sort array
  sortArray(inputAr);

  // finding missing number here
  var result = 0;
  if (inputAr[0] > 1 || inputAr[inputAr.length - 1] < 1) {
    result = 1;
  } else {
    for (var i = 0; i < inputAr.length; i++) {
      if ((inputAr[i + 1] - inputAr[i]) > 1) {
        result = inputAr[i] + 1;
      }
    }
  }
  if (!result) {
    result = inputAr[inputAr.length - 1] + 1;
  }
  return result;
}

function sortArray(inputAr) {
  var temp;
  for (var i = 0; i < inputAr.length; i++) {
    for (var j = i + 1; j < inputAr.length; j++) {
      if (inputAr[j] < inputAr[i]) {
        temp = inputAr[j];
        inputAr[j] = inputAr[i];
        inputAr[i] = temp;
      }
    }
  }
}

console.log(findMissingNumber([1, 3, 6, 4, 1, 2]));
console.log(findMissingNumber([1, 2, 3]));
console.log(findMissingNumber([85]));
console.log(findMissingNumber([86, 85]));
console.log(findMissingNumber([0, 1000]));

Answer 6

let missing = [];
let numArray = [3,5,1,8,9,36];
const sortedNumArray = numArray.sort((a, b) => a - b);
sortedNumArray.reduce((acc, current) => {
  let next = acc + 1;
  if (next !== current) {
    for(next; next < current; next++) {
      missing.push(next);
    }
  }
  return current;
});