Formatted question description: https://leetcode.ca/all/415.html

415. Add Strings (Easy)

Given two non-negative integers num1 and num2 represented as string, return the sum of num1 and num2.

Note:

The length of both num1 and num2 is < 5100.
Both num1 and num2 contains only digits 0-9.
Both num1 and num2 does not contain any leading zero.
You must not use any built-in BigInteger library or convert the inputs to integer directly.

Related Topics:
Math

Similar Questions:

Solution 1.

class Solution {
    public String addStrings(String num1, String num2) {
        if (num1.equals("0") && num2.equals("0"))
            return "0";
        int length1 = num1.length(), length2 = num2.length();
        while (num1.length() < length2)
            num1 = "0" + num1;
        while (num2.length() < length1)
            num2 = "0" + num2;
        int totalLength = Math.max(length1, length2) + 1;
        int[] sumArray = new int[totalLength];
        for (int i = totalLength - 1; i > 0; i--) {
            int digit1 = num1.charAt(i - 1) - '0';
            int digit2 = num2.charAt(i - 1) - '0';
            sumArray[i] += digit1 + digit2;
            if (sumArray[i] >= 10) {
                sumArray[i - 1] += sumArray[i] / 10;
                sumArray[i] %= 10;
            }
        }
        StringBuffer sb = new StringBuffer();
        if (sumArray[0] != 0)
            sb.append(sumArray[0]);
        for (int i = 1; i < totalLength; i++)
            sb.append(sumArray[i]);
        String sum = sb.toString();
        return sum;
    }
}

############

class Solution {
    public String addStrings(String num1, String num2) {
        int i = num1.length() - 1, j = num2.length() - 1;
        StringBuilder ans = new StringBuilder();
        for (int c = 0; i >= 0 || j >= 0 || c > 0; --i, --j) {
            int a = i < 0 ? 0 : num1.charAt(i) - '0';
            int b = j < 0 ? 0 : num2.charAt(j) - '0';
            c += a + b;
            ans.append(c % 10);
            c /= 10;
        }
        return ans.reverse().toString();
    }

    public String subStrings(String num1, String num2) {
        int m = num1.length(), n = num2.length();
        boolean neg = m < n || (m == n && num1.compareTo(num2) < 0);
        if (neg) {
            String t = num1;
            num1 = num2;
            num2 = t;
        }
        int i = num1.length() - 1, j = num2.length() - 1;
        StringBuilder ans = new StringBuilder();
        for (int c = 0; i >= 0; --i, --j) {
            c = (num1.charAt(i) - '0') - c - (j < 0 ? 0 : num2.charAt(j) - '0');
            ans.append((c + 10) % 10);
            c = c < 0 ? 1 : 0;
        }
        while (ans.length() > 1 && ans.charAt(ans.length() - 1) == '0') {
            ans.deleteCharAt(ans.length() - 1);
        }
        if (neg) {
            ans.append('-');
        }
        return ans.reverse().toString();
    }
}

// OJ: https://leetcode.com/problems/add-strings/
// Time: O(M + N)
// Space: O(1)
class Solution {
public:
    string addStrings(string a, string b) {
        string sum;
        int carry = 0;
        auto i = a.rbegin(), j = b.rbegin();
        while (i != a.rend() || j != b.rend() || carry) {
            if (i != a.rend()) carry += *i++ - '0';
            if (j != b.rend()) carry += *j++ - '0';
            sum += (carry % 10) + '0';
            carry /= 10;
        }
        reverse(sum.begin(), sum.end());
        return sum;
    }
};

class Solution:
    def addStrings(self, num1: str, num2: str) -> str:
        i, j = len(num1) - 1, len(num2) - 1
        ans = []
        c = 0
        while i >= 0 or j >= 0 or c:
            a = 0 if i < 0 else int(num1[i])
            b = 0 if j < 0 else int(num2[j])
            c, v = divmod(a + b + c, 10) # nice
            ans.append(str(v))
            i, j = i - 1, j - 1
        return "".join(ans[::-1])

    # follow-up, substract
    def subStrings(self, num1: str, num2: str) -> str:
        m, n = len(num1), len(num2)
        neg = m < n or (m == n and num1 < num2)
        if neg:
            num1, num2 = num2, num1
        i, j = len(num1) - 1, len(num2) - 1
        ans = []
        c = 0
        while i >= 0:
            c = int(num1[i]) - c - (0 if j < 0 else int(num2[j]))
            ans.append(str((c + 10) % 10))
            c = 1 if c < 0 else 0
            i, j = i - 1, j - 1
        
        # eg. 99199 - 99198 = 1, ans here is "10000"
        while len(ans) > 1 and ans[-1] == "0":
            ans.pop()
        if neg: # will not be "-0", neg only when <0
            ans.append("-")
        return "".join(ans[::-1])

############

class Solution(object):
  def addStrings(self, num1, num2):
    """
    :type num1: str
    :type num2: str
    :rtype: str
    """
    carry = 0
    i = len(num1) - 1
    j = len(num2) - 1
    ans = ""
    for k in reversed(range(0, max(len(num1), len(num2)))):
      a = int(num1[i]) if i >= 0 else 0
      b = int(num2[j]) if j >= 0 else 0
      i, j = i - 1, j - 1
      c = carry
      carry = 0
      sum = a + b + c
      if sum >= 10:
        carry = 1
        ans += str(sum - 10)
      else:
        ans += str(sum)
    if carry == 1:
      ans += "1"
    return ans[::-1]

func addStrings(num1 string, num2 string) string {
	i, j := len(num1)-1, len(num2)-1
	ans := []byte{}
	for c := 0; i >= 0 || j >= 0 || c > 0; i, j = i-1, j-1 {
		if i >= 0 {
			c += int(num1[i] - '0')
		}
		if j >= 0 {
			c += int(num2[j] - '0')
		}
		ans = append(ans, byte(c%10+'0'))
		c /= 10
	}
	for i, j := 0, len(ans)-1; i < j; i, j = i+1, j-1 {
		ans[i], ans[j] = ans[j], ans[i]
	}
	return string(ans)
}

func subStrings(num1 string, num2 string) string {
	m, n := len(num1), len(num2)
	neg := m < n || (m == n && num1 < num2)
	if neg {
		num1, num2 = num2, num1
	}
	i, j := len(num1)-1, len(num2)-1
	ans := []byte{}
	for c := 0; i >= 0; i, j = i-1, j-1 {
		c = int(num1[i]-'0') - c
		if j >= 0 {
			c -= int(num2[j] - '0')
		}
		ans = append(ans, byte((c+10)%10+'0'))
		if c < 0 {
			c = 1
		} else {
			c = 0
		}
	}
	for len(ans) > 1 && ans[len(ans)-1] == '0' {
		ans = ans[:len(ans)-1]
	}
	if neg {
		ans = append(ans, '-')
	}
	for i, j := 0, len(ans)-1; i < j; i, j = i+1, j-1 {
		ans[i], ans[j] = ans[j], ans[i]
	}
	return string(ans)
}

function addStrings(num1: string, num2: string): string {
    const res = [];
    let i = num1.length - 1;
    let j = num2.length - 1;
    let isOver = false;
    while (i >= 0 || j >= 0 || isOver) {
        const x = Number(num1[i--]) || 0;
        const y = Number(num2[j--]) || 0;
        const sum = x + y + (isOver ? 1 : 0);
        isOver = sum >= 10;
        res.push(sum % 10);
    }
    return res.reverse().join('');
}

/**
 * @param {string} num1
 * @param {string} num2
 * @return {string}
 */
var addStrings = function (num1, num2) {
    let i = num1.length - 1;
    let j = num2.length - 1;
    const ans = [];
    for (let c = 0; i >= 0 || j >= 0 || c; --i, --j) {
        c += i < 0 ? 0 : parseInt(num1.charAt(i), 10);
        c += j < 0 ? 0 : parseInt(num2.charAt(j), 10);
        ans.push(c % 10);
        c = Math.floor(c / 10);
    }
    return ans.reverse().join('');
};

/**
 * @param {string} num1
 * @param {string} num2
 * @return {string}
 */
var subStrings = function (num1, num2) {
    const m = num1.length;
    const n = num2.length;
    const neg = m < n || (m == n && num1 < num2);
    if (neg) {
        const t = num1;
        num1 = num2;
        num2 = t;
    }
    let i = num1.length - 1;
    let j = num2.length - 1;
    const ans = [];
    for (let c = 0; i >= 0; --i, --j) {
        c = parseInt(num1.charAt(i), 10) - c;
        if (j >= 0) {
            c -= parseInt(num2.charAt(j), 10);
        }
        ans.push((c + 10) % 10);
        c = c < 0 ? 1 : 0;
    }
    while (ans.length > 1 && ans[ans.length - 1] == '0') {
        ans.pop();
    }
    if (neg) {
        ans.push('-');
    }
    return ans.reverse().join('');
};

impl Solution {
    pub fn add_strings(num1: String, num2: String) -> String {
        let mut res = vec![];
        let s1 = num1.as_bytes();
        let s2 = num2.as_bytes();
        let (mut i, mut j) = (s1.len(), s2.len());
        let mut is_over = false;
        while i != 0 || j != 0 || is_over {
            let mut sum = if is_over { 1 } else { 0 };
            if i != 0 {
                sum += (s1[i - 1] - b'0') as i32;
                i -= 1;
            }
            if j != 0 {
                sum += (s2[j - 1] - b'0') as i32;
                j -= 1;
            }
            is_over = sum >= 10;
            res.push((sum % 10).to_string());
        }
        res.into_iter().rev().collect()
    }
}

415 - Add Strings

415. Add Strings (Easy)

Solution 1.

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415. Add Strings (Easy)

Solution 1.

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