# Complete Equation by Filling Missing Operator in JavaScript

We are required to write a JavaScript function that takes in a bunch of numbers and returns the correct sequence of operations to satisfy the equation. The operator that can be used are (+, −, *, /, ^, %).

For example −

Input : 5 3 8          Output : 5+3=8
Input : 9 27 3         Output : 9=27/3
Input : 5 2 25 , 1 5 2 Output : 5^2=25 , 1=5%2

For each input, there is at least one possible sequence, we are required to return at least one correct sequence.

The algorithm we are going to use to solve this problem is −

• Firstly, we choose the bigger number on one of the sides like in 1 4 7 it would be 7

• Then we put an equal to facing the middle. Like 1 4 7 it would be 1 4=7

• Lastly, we solve the equation

• If that doesn't work, we try the other number

## Example

The code for this will be −

const arr = ["5 3 8", "9 27 3", "5 2 25", "1 5 2", "3 3 3 30"];
const findCombination = (arr = []) => {
for(let i = 0; i < arr.length; i++){
const el = arr[i];
// using brute force to try solutions
for(let n = 0; n < 1000; n++){
const s = el.replace(/ /g, () => "+−
*/^%="[Math.floor(Math.random() * 7)]);
if(eval(s.replace(/=/g, "===").replace(/\^/g, "**")) === true
};
};
}
};
console.log(findCombination(arr));

## Output

And the output in the console will be −

[
'5+3=8',
'9=27/3',
'5^2=25',
'1=5%2',
'3=3%3^30',
'3^3+3=30',
'3+3^3=30'
]

Updated on: 21-Nov-2020

260 Views