[LeetCode] 415. Add Strings

String concatenation. That topic is still on. 43 shadow problem . example,

"13" + "79" = "92"

This problem does not have any algorithm, the study is related to the operation of the string. Java and JS practice a little there are some differences. Because of the relationship between StringBuilder, so the numbers on the inside of each and every result can be append in Java; JS there is an array instead of StringBuilder function. But the two languages ​​to realize the idea is the same.

Time O (n)

Space O (n)

Java implementation

 1 class Solution {
 2     public String addStrings(String num1, String num2) {
 3         int i = num1.length() - 1;
 4         int j = num2.length() - 1;
 5         int carry = 0;
 6         StringBuilder sb = new StringBuilder();
 7         while (i >= 0 || j >= 0 || carry == 1) {
 8             int a = i >= 0 ? num1.charAt(i--) - '0' : 0;
 9             int b = j >= 0 ? num2.charAt(j--) - '0' : 0;
10             int sum = a + b + carry;
11             sb.append(sum % 10);
12             carry = sum / 10;
13         }
14         return sb.reverse().toString();
15     }
16 }

 

JavaScript implementation

 1 /**
 2  * @param {string} num1
 3  * @param {string} num2
 4  * @return {string}
 5  */
 6 var addStrings = function(num1, num2) {
 7     let i = num1.length - 1;
 8     let j = num2.length - 1;
 9     let carry = 0;
10     let res = [];
11     while (i >= 0 || j >= 0 || carry == 1) {
12         let digit1 = i < 0 ? 0 : num1.charAt(i) - '0';
13         let digit2 = j < 0 ? 0 : num2.charAt(j) - '0';
14         let digitsSum = digit1 + digit2 + carry;
15         res.push(digitsSum % 10);
16         carry = Math.floor(digitsSum / 10);
17         i--;
18         j--;
19     }
20     return res.reverse().join('');
21 };