415_Add_Strings

qiyuangong · qiyuangong · commit 662ee2e944b1 · 2018-12-01T10:35:56.000+08:00
diff --git a/README.md b/README.md
@@ -131,6 +131,7 @@ Also, there are open source implementations for basic data structs and algorithm
 | 408 | [Valid Word Abbreviation](https://leetcode.com/problems/valid-word-abbreviation/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/408_Valid_Word_Abbreviation.py) | Go over abbr and word, O(n) and O(1) |
 | 409 | [Longest Palindrome](https://leetcode.com/problems/longest-palindrome/description/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/409_Longest_Palindrome.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/409_Longest_Palindrome.java) | Length of Palindrome is always 2n or 2n + 1. So, get all possible 2*n, and choose a single one as 1 if it exists. |
 | 412 | [Fizz Buzz](https://leetcode.com/problems/fizz-buzz/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/412_Fizz_Buzz.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/412_Fizz_Buzz.java) | 1. From 1 to n, condition check<br>2. Condition check and string connect |
+| 415 | [Add Strings](https://leetcode.com/problems/add-strings/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/415_Add_Strings.py) [Java](https://github.com/qiyuangong/leetcode/blob/master/java/415_Add_Strings.java) | Two points, careful abour carry, O(n) and O(n) |
 | 416 | [Partition Equal Subset Sum](https://leetcode.com/problems/partition-equal-subset-sum/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/416_Partition_Equal_Subset_Sum.py) | DP, Check if sum of some elements can be half of total sum, O(total_sum / 2 * n) and O(total_sum / 2) |
 | 421 | [Maximum XOR of Two Numbers in an Array](https://leetcode.com/problems/maximum-xor-of-two-numbers-in-an-array/) | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/421_Maximum_XOR_of_Two_Numbers_in_an_Array.py) | Check 0~32 prefix, check if there is x y in prefixes, where x ^ y = answer ^ 1, O(32n) and O(n) |
 | 422 | [Valid Word Square](https://leetcode.com/problems/valid-word-square/) &hearts; | [Python](https://github.com/qiyuangong/leetcode/blob/master/python/422_Valid_Word_Square.py) | Compare row with column, O(n^2) |
diff --git a/java/415_Add_Strings.java b/java/415_Add_Strings.java
@@ -0,0 +1,15 @@
+public class Solution {
+    public String addStrings(String num1, String num2) {
+        StringBuilder sb = new StringBuilder();
+        int carry = 0;
+        // condition is great
+        // https://leetcode.com/problems/add-strings/discuss/90436/Straightforward-Java-8-main-lines-25ms
+        for(int i = num1.length() - 1, j = num2.length() - 1; i >= 0 || j >= 0 || carry == 1; i--, j--){
+            int x = i < 0 ? 0 : num1.charAt(i) - '0';
+            int y = j < 0 ? 0 : num2.charAt(j) - '0';
+            sb.append((x + y + carry) % 10);
+            carry = (x + y + carry) / 10;
+        }
+        return sb.reverse().toString();
+    }
+}
diff --git a/python/415_Add_Strings.py b/python/415_Add_Strings.py
@@ -0,0 +1,53 @@
+class Solution(object):
+    # def addStrings(self, num1, num2):
+    #     """
+    #     :type num1: str
+    #     :type num2: str
+    #     :rtype: str
+    #     """
+    #     if num1 is None:
+    #         num1 = '0'
+    #     if num2 is None:
+    #         num2 = '0'
+    #     res = []
+    #     carry = 0
+    #     ls = min(len(num1), len(num2))
+    #     pos = -1
+    #     while pos + ls >= 0:
+    #         curr = int(num1[pos]) + int(num2[pos]) + carry
+    #         res.insert(0, str(curr % 10))
+    #         carry = curr / 10
+    #         pos -= 1
+    #     while pos + len(num1) >= 0:
+    #         curr = int(num1[pos]) + carry
+    #         res.insert(0, str(curr % 10))
+    #         carry = curr / 10
+    #         pos -= 1
+    #     while pos + len(num2) >= 0:
+    #         curr = int(num2[pos]) + carry
+    #         res.insert(0, str(curr % 10))
+    #         carry = curr / 10
+    #         pos -= 1
+    #     if carry != 0:
+    #         res.insert(0, str(carry))
+    #     return ''.join(res)
+
+    def addStrings(self, num1, num2):
+        res = []
+        pos1 = len(num1) - 1
+        pos2 = len(num2) - 1
+        carry = 0
+        # This conditon is great
+        # https://leetcode.com/problems/add-strings/discuss/90436/Straightforward-Java-8-main-lines-25ms
+        while pos1 >= 0 or pos2 >= 0 or carry == 1:
+            digit1 = digit2 = 0
+            if pos1 >= 0:
+                digit1 = ord(num1[pos1]) - ord('0')
+            if pos2 >= 0:
+                digit2 = ord(num2[pos2]) - ord('0')
+            res.append(str((digit1 + digit2 + carry) % 10))
+            carry = (digit1 + digit2 + carry) / 10
+            pos1 -= 1
+            pos2 -= 1
+        # reverse res
+        return ''.join(res[::-1])
