415. Add Strings

大数相加

逐个相加Math.max(m, n)次

• Runtime: 88 ms, faster than 77.02%
• Memory Usage: 39.5 MB, less than 29.59%
• 时间复杂度
• 空间复杂度

/**
 * @param {string} num1
 * @param {string} num2
 * @return {string}
 */
var addStrings = function(num1, num2) {
    let m = num1.length - 1
    let n = num2.length - 1
    let carry = 0
    let res = ''
    while(m >= 0 || n >= 0 || carry !== 0) {
        let x = m < 0 ? 0 : (num1[m--] - '0')
        let y = n < 0 ? 0 : (num2[n--] - '0')
        let sum = x + y + carry
        carry = parseInt(sum / 10)
        res = (sum % 10) + res
    }
    return res
};

逐个相加Math.min(m, n) + 1次

• Runtime: 84 ms, faster than 89.03%
• Memory Usage: 39.5 MB, less than 27.42%
• 时间复杂度
• 空间复杂度

/**
 * @param {string} num1
 * @param {string} num2
 * @return {string}
 */
var addStrings = function(num1, num2) {
    let m = num1.length - 1
    let n = num2.length - 1
    let res = ''
    let carry = 0
    while((m >= 0 && n >= 0) || carry !== 0) {
        let x = m < 0 ? 0 : (num1[m--] - '0')
        let y = n < 0 ? 0 : (num2[n--] - '0')
        let temp = x + y + carry
        carry = parseInt(temp / 10)
        res = temp % 10 + res
    }
    if(m >= 0) res = num1.substr(0, m + 1) + res
    if(n >= 0) res = num2.substr(0, n + 1) + res
    return res
};