Given two non-negative integers, num1 and num2 represented as string, return the sum of num1 and num2 as a string.
You must solve the problem without using any built-in library for handling large integers (such as BigInteger). You must also not convert the inputs to integers directly.
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| Example 1:
Input: num1 = "11", num2 = "123"
Output: "134"
Example 2:
Input: num1 = "456", num2 = "77"
Output: "533"
Example 3:
Input: num1 = "0", num2 = "0"
Output: "0"
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Constraints:
- 1 <= num1.length, num2.length <= 104
- num1 and num2 consist of only digits.
- num1 and num2 don’t have any leading zeros except for the zero itself.
Solution#
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| class Solution {
public String addStrings(String num1, String num2) {
int carry = 0;
int idx1 = num1.length() - 1;
int idx2 = num2.length() - 1;
StringBuilder sb = new StringBuilder();
while (idx1 >= 0 || idx2 >= 0) {
int digit1 = (idx1 >= 0) ? num1.charAt(idx1) - '0': 0; // 0 1
int digit2 = (idx2 >= 0) ? num2.charAt(idx2) - '0': 0; // 1 2
// 4 = 1 + 3
// 3 = 1 + 2
int value = digit1 + digit2 + carry;
carry = value / 10;
value = value % 10;
sb.append(value);
idx1--;
idx2--;
}
if (carry == 1) {
sb.append(1);
}
return sb.reverse().toString();
}
}
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Solution 2021-10-20#
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| class Solution {
public String addStrings(String num1, String num2) {
int carry = 0;
int len1 = num1.length();
int len2 = num2.length();
int i = len1 - 1;
int j = len2 - 1;
StringBuilder sb = new StringBuilder();
while (i >= 0 || j >= 0) {
int c1 = i >= 0 ? num1.charAt(i) - '0' : 0;
int c2 = j >= 0 ? num2.charAt(j) - '0': 0;
int val = c1 + c2 + carry;
carry = val / 10;
val = val % 10;
sb.append(val);
i--;
j--;
}
if (carry > 0) {
sb.append(carry);
}
return sb.reverse().toString();
}
}
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