题解 | #高精度整数加法#

//数字超过了NUMBER.MAX_SAFE_INTEGER，所以这里使用对位相加，写的有点烂，凑活看
let arr = []
let n = 2;
while(line = readline()) {
    arr.push(line);
}

for (let i = 0; i<arr.length/n; i++) {
    let list = arr.slice(n*i, n*(i+1));
    let a = list[0];
    let b = list[1];
    let long = a.length > b.length ? a : b; // 这里判断长短
    let short = long == a ? b : a;
    let diffL = long.length - short.length;
    let diffS = diffL ? long.substr(0, diffL) : ''; // 获取长的字符串多出的部分
    let newLong = long.substring(diffL);
    let combineStr = combine(newLong, short, diffS);
    print(combineStr)
}

function combine(str1, str2, diffS) {
    let arr1 = str1.split('').reverse();
    let arr2 = str2.split('').reverse();
    let arr3 = new Array(arr1.length + 1).fill(0); // 存储两个等长相加的字符串
    for (let i= 0; i<arr1.length; i++) {
        let num  = arr3[i] + parseInt(arr1[i]) + parseInt(arr2[i]);
        if (num >= 10) {
            arr3[i + 1] = arr3[i + 1] + 1;
            arr3[i] = num - 10;
        } else {
            arr3[i] = num;
        }
    }
    let lastNum = arr3.pop(); // 判断最高位是1还是0

    if (lastNum == 0) {
        return diffS + arr3.reverse().join('');
    } else {
        if (diffS.length) {
            let arr = diffS.split('').reverse().map(x => parseInt(x));
            arr[0]  = arr[0] + 1;
            for (let i= 0; i<arr.length; i++) { 
                if(arr[i] >= 10) {
                    arr[i + 1]  = arr[i + 1] + 1;
                    arr[i] = arr[i] - 10;
                }
            }
            return arr.reverse().join('') + arr3.reverse().join('');
        }
        else {
            return  '1'+ arr3.reverse().join('');
        }
    }
}