Leet Code: Add Two Numbers

add_two_ln.js

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
function listLength(lst){
    let output = 0;
    let current = lst;
    while(current != null){
        output +=1;
        current = current.next;
    }
    return output;
}

function getIndex(i, lst){
    let current = lst;
    if(i == 0){
        return current.val;
    }else{
        while(i != 0 && current.next != null){
            current = current.next;
            i--;
        }
        return current.val;
    }
}

var addTwoNumbers = function(l1, l2) {
    const ls1Len = listLength(l1);
    const ls2Len = listLength(l2);
    const mxLen = Math.max(ls1Len, ls2Len);
    let carry = 0;
    let res = "";
    for(let i = 0; i <= mxLen-1; i++){    
        let l = 0;
        let r = 0;
        if(i <= ls1Len-1){
            l = getIndex(i, l1);
        }
        if(i <= ls2Len-1){
            r = getIndex(i, l2);
        }
        
        let sum = l + carry + r;
        if(sum >= 10){
            carry = 1;
            
            res += sum - 10;
        }else{
            res += sum;
            carry = 0;
        }
    }
    if(carry != 0){
        res += 1;
    }

    let sumArray = res.split("");
    let head = new ListNode();
    current = head;
    for(let i=0; i <= sumArray.length-1; i++){
        current.val = sumArray[i].trim();
        if(i != sumArray.length-1){
          current.next = new ListNode();
          current = current.next;
        }
    }
    return head;
};