Dehaat

const a = [['a', 2], ['a', 3], ['c', 4]];
const b = [['a', 4], ['a', 4], ['a', 4], ['c', 3], ['c', 4]];

// map = {
//   'a': [4],
//   'c': [3,4]
// }

map1 = {
    'a': [2],
    'b': [3],
    'c': [4]
}

map2 = {
    'a': [4],
    'c': [3,4]
}


// 2*4 + 4*3 + 4*4
// 8+12+16

function findSum(arr1, arr2) {
    const charMapping = {}
    for (let i=0; i< arr2.length; ++i) {
        const char = arr2[i][0];
        if (charMapping[char] !== undefined) {
            charMapping[char].push(arr2[i][1]);
        } else {
            charMapping[char] = [arr2[i][1]]
        }
    }
    
    let sum = 0;
    for (let i=0; i<arr1.length; ++i) {
        const char = arr1[i][0];
        if (charMapping[char] !== undefined) {
            const arr3 = charMapping[char];
            for (let j=0; j<arr3.length; ++j) {
                sum += arr1[i][1]*arr3[j];
            }
        }
    }
    
    return sum;
}

console.log(findSum(a,b))

// const demoPromiseSuccess2secs = new Promis((res, rej) => {
//     setTimeout(() => { res("done") }, 2000)
// })

// const demoPromiseFail2secs = new Promis((res, rej) => {
//     setTimeout(() => { rej("failed") }, 2000)
// })


// async function demo() {
    
//     demoPromiseSuccess2secs
//     .then(data => { console.log(data)})
//     .catch(err => { console.log(err)})
    
//     try {
//         const data = await demoPromiseSuccess2secs();
//     } catch (err) {
//         // handle err
//     }
    
// }