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 numArray = [0189459, 0189460, 0189461, 0189463, 0189465];

For the array above I would need 0189462 and 0189464 logged out.

UPDATE : this is the exact solution I used from Soufiane's answer.

var numArray = [0189459, 0189460, 0189461, 0189463, 0189465];
var mia= [];

    for(var i = 1; i < numArray.length; i++) 
    {     
        if(numArray[i] - numArray[i-1] != 1) 
        {         
            var x = numArray[i] - numArray[i-1];
            var j = 1;
            while (j<x)
            {
                mia.push(numArray[i-1]+j);
                j++;
            }
        }
    }
alert(mia) // returns [0189462, 0189464]

UPDATE

Here's a neater version using .reduce

var numArray = [0189459, 0189460, 0189461, 0189463, 0189466];
var mia = numArray.reduce(function(acc, cur, ind, arr) {
  var diff = cur - arr[ind-1];
  if (diff > 1) {
    var i = 1;
    while (i < diff) {
      acc.push(arr[ind-1]+i);
      i++;
    }
  }
  return acc;
}, []);
console.log(mia);

Answer 1

Please check below code.....

function solution(A) {
   var max = Math.max.apply(Math, A);
   if(A.indexOf(1)<0) return 1;
   var t = (max*(max+1)/2) - A.reduce(function(a,b){return a+b});
   return t>0?t:max+1;
}

Answer 2

If you know that the numbers are sorted and increasing:

for(var i = 1; i < numArray.length; i++) {
    if(numArray[i] - numArray[i-1] != 1) {
           //Not consecutive sequence, here you can break or do whatever you want
    }
}

Answer 3

Here's a variant of @Mark Walters's function which adds the ability to specify a lower boundary for your sequence, for example if you know that your sequence should always begin at 0189455, or some other number like 1.

It should also be possible to adjust this code to check for an upper boundary, but at the moment it can only look for lower boundaries.

//Our first example array.
var numArray = [0189459, 0189460, 0189461, 0189463, 0189465];
//For this array the lowerBoundary will be 0189455
var numArrayLowerBoundary = 0189455;

//Our second example array.
var simpleArray = [3, 5, 6, 7, 8, 10, 11, 13];
//For this Array the lower boundary will be 1
var simpleArrayLowerBoundary = 1;

//Build a html string so we can show our results nicely in a div
var html = "numArray = [0189459, 0189460, 0189461, 0189463, 0189465]<br>"
html += "Its  lowerBoundary is \"0189455\"<br>"
html += "The following numbers are missing from the numArray:<br>"
html += findMissingNumbers(numArray, numArrayLowerBoundary);
html += "<br><br>"
html += "simpleArray = [3, 5, 6, 7, 8, 10, 11, 13]<br>"
html += "Its  lowerBoundary is \"1\".<br>"
html += "The following numbers are missing from the simpleArray:<br>"
html += findMissingNumbers(simpleArray, simpleArrayLowerBoundary);

//Display the results in a div
document.getElementById("log").innerHTML=html;

//This is the function used to find missing numbers!
//Copy/paste this if you just want the function and don't need the demo code.
function findMissingNumbers(arrSequence, lowerBoundary) {
  var mia = [];
  for (var i = 0; i < arrSequence.length; i++) {
    if (i === 0) {
      //If the first thing in the array isn't exactly
      //equal to the lowerBoundary...
      if (arrSequence[i] !== lowerBoundary) {
        //Count up from lowerBoundary, incrementing 1
        //each time, until we reach the
        //value one less than the first thing in the array.
        var x = arrSequence[i];
        var j = lowerBoundary;
        while (j < x) {
          mia.push(j); //Add each "missing" number to the array
          j++;
        }
      } //end if
    } else {
      //If the difference between two array indexes is not
      //exactly 1 there are one or more numbers missing from this sequence.
      if (arrSequence[i] - arrSequence[i - 1] !== 1) {
        //List the missing numbers by adding 1 to the value
        //of the previous array index x times.
        //x is the size of the "gap" i.e. the number of missing numbers
        //in this sequence.      
        var x = arrSequence[i] - arrSequence[i - 1];
        var j = 1;
        while (j < x) {
          mia.push(arrSequence[i - 1] + j); //Add each "missing" num to the array
          j++;
        }
      } //end if
    } //end else
  } //end for
  //Returns any missing numbers, assuming that lowerBoundary is the
  //intended first number in the sequence.
  return mia;
}

<div id="log"></div> <!-- Just used to display the demo code -->

Answer 4

I use a recursive function for this.

function findMissing(arr, start, stop) {

    var current = start,
        next = stop,
        collector = new Array();

    function parseMissing(a, key) {
        if(key+1 == a.length) return;

        current = a[key];
        next = a[key + 1];

        if(next - current !== 1) {
            collector.push(current + 1);
            // insert current+1 at key+1
            a = a.slice( 0, key+1 ).concat( current+1 ).concat( a.slice( key +1 ) );
            return parseMissing(a, key+1);
        }

        return parseMissing(a, key+1);
    }

    parseMissing(arr, 0);
    return collector;
}

Not the best idea if you are looking through a huge set of numbers. FAIR WARNING: recursive functions are resource intensive (pointers and stuff) and this might give you unexpected results if you are working with huge numbers. You can see the jsfiddle. This also assumes you have the array sorted.

Basically, you pass the "findMissing()" function the array you want to use, the starting number and stopping number and let it go from there.

So:

var missingArr = findMissing(sequenceArr, 1, 10);

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

Try as shown below

// Find the missing number
let numArray = [0189459, 0189460, 0189461, 0189463, 0189468];
let numLen = numArray.length;
let actLen = Number(numArray[numLen-1])-Number(numArray[0]);
let  allNumber = [];

for(let i=0; i<=actLen; i++){
  allNumber.push(Number(numArray[0])+i);
}
[...allNumber].forEach(ele=>{
  if(!numArray.includes(ele)){
    console.log('Missing Number -> '+ele);
  }
})