415.add-strings.js

/*
 * @lc app=leetcode.cn id=415 lang=javascript
 *
 * [415] Add Strings
 */

// @lc code=start
/**
 * @param {string} num1
 * @param {string} num2
 * @return {string}
 */
/*
1 2 3 i
  4 9 j

1 7 2 

 */
var addStrings = function(num1, num2) {
    let len1 = num1.length;
    let len2 = num2.length;
    let i = len1 - 1;
    let j = len2 - 1;
    let carry = 0; // 进位
    let ans = '';
    while (i >= 0 || j >= 0) {
        let curr1 = i < 0 ? 0 : num1[i] * 1;
        let curr2 = j < 0 ? 0 : num2[j] * 1;
        let { result, nextCarry } = add(curr1, curr2, carry);
        carry = nextCarry;
        ans = result + ans;
        i--;
        j--;
    }
    if (carry !== 0) {
        ans = carry + ans;
    }
    return ans;
};

function add(n1, n2, lastCarry) {
    let nextCarry = 0;
    let result = 0;
    let sum = n1 + n2 + lastCarry;
    if (sum >= 10) {
        let strSum = String(sum);
        result = strSum.slice(1) * 1;
        nextCarry = strSum.slice(0, 1) * 1;
    } else {
        result = sum
    }
    return {
        result,
        nextCarry
    }
}
// @lc code=end