// 思路：
// 1. 以0补齐两个字符串，保证长度一致
// 2. 存储进位信息，每次相加加上他
// 3. 存储下一次进位信息
// 4. 算出对应位数相加取余数，加到字符串上
function addBigNum(s1,s2) {
    let num = Math.max(s1.length,s2.length);
    s1 = s1.padStart(num,0);
    s2 = s2.padStart(num,0);
    // 存储进位信息
    let c = 0;
    let res = '';
    for(let i = num -1;i>=0;i--) {
        let g = parseInt(s1[i]) + parseInt(s2[i]) + c;
        c = Math.floor(g / 10);
        g = g % 10;
        res = g + res;
    }
    if(c === 1) {
        res = 1 + res;
    }
    return res;
}

let s1 = '11111',s2 = '912222';
console.log(addBigNum(s1,s2))