//Given alist of numbers and a number x, return whether any two numbers from the list add up to x. For example, 
//given [10, 15, 3, 7] and x of 17, return true since 10 + 7 is equal to 17.

//The Two Loop Method
function findSumA(numbers, answer){
    //Loop through the array and add the adjacent number and check for the answer
    let checkValue = 0;
    let found = false;

    //[] startindex = 0,
    for (let i = 0; i <= numbers.length -2; i++) {
        //Loop Over the array in the adjacent after the current value
        for(let y = (i + 1); y <= numbers.length - 1; y++){
            if(answer == numbers[i] + numbers[y]){
                found = true;
                return found;
            }
        }  
    }
    return found;
}

//Reordered Array Method
function findSumB(numbers, answer){
    let found = false;
    let checkValue = 0;
    //sort the array
    numbers.sort(function(a,b){
        return a-b
    });
    let startIndex = 0;
    let endIndex = numbers.length - 1;
    do{
        checkValue = numbers[startIndex] + numbers[endIndex]
        if(answer == checkValue){
            found = true;
            break;
        }
        else if(answer > checkValue){
            startIndex++;
        }
        else if(answer < checkValue){
            endIndex --;
        }

    } while(found == false && startIndex < endIndex);

    return found;

}

//Efficient Solution
function findSumC(numbers, answer){
    let checkValue = 0;
    let found= false;
    for(let i = 0; i <= numbers.length - 1; i++){
        checkValue = answer - numbers[i];
        if(numbers.includes(checkValue, i + 1)){
            found= true;
            break;
        }
    }
    return found;
}

//Return All Combinations Method
function findSumD(numbers, answer){
    let checkValue = 0;
    let checkIndex = -1;
    let ansArray = [];

    for(let i = 0; i < numbers.length - 1; i++){
        checkValue = answer - numbers[i];
        checkIndex = numbers.indexOf(checkValue);

        if(checkIndex !=-1 && checkIndex !=i){
            //add the 2 numbers to the array
            ansArray.push(numbers[i] + " + " + checkValue);
            //remove the duplicates
            numbers.splice(checkIndex, 1);
        }
    }
    return ansArray;
}

function displaySum(){
    let answer = document.getElementById("sumValue").value;
    // let numArray = [10,15,3,7];

    let numArray = generateNumbers(20);

    //show the array on the screen

    document.getElementById("numList").innerHTML = numArray.toString();
    let found = findSumC(numArray, answer);
    document.getElementById("results").innerHTML = found.toString();
}

function displayAllSums(){
    let answer = document.getElementById("sumValue").value;
    let numArray = generateNumbers(20);
    
    // let numArray =[10,7,15,3,16];

    //show the array on the screen

    document.getElementById("numList").innerHTML = numArray.toString();
    let found = findSumD(numArray, answer).join("
");
    document.getElementById("results").innerHTML = found.toString();
}

//Generate Random Array of Numbers
function generateNumbers(max){
    var arr = [];
    while (arr.length < max){
        var r = Math.floor(Math.random() * 100) + 1;
        if (arr.indexOf(r) == -1){
            arr.push(r);
        }
    }
    return arr;
}
                

The Sum of All Fears

Displayed here are four different solutions to The Sum of All Fears coding challenge. I go through the most straight-forward methods to the most efficient. I also included a function that generates an array of 20 random numbers to avoid hard coding a selected list. This way users can see for themselves the different combinations that may yield the answer to the number they seek.

In the Two Loop Method, the most straight-forward approach, I nest a for-loop inside of another for-loop in order to compare the beginning index to each subsequent index. If no result is found true, the following index is compared to the subsequent indices. This process continues until a combination is either found true otherwise it returns false.

The Reordered Array Method