415

idf · idf · commit d34e28995731 · 2019-01-02T15:16:00.000-08:00
diff --git a/415 Add Strings.py b/415 Add Strings.py
@@ -0,0 +1,56 @@
+#!/usr/bin/python3
+"""
+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.
+"""
+
+
+class Solution:
+    def int(self, n):
+        return ord(n) - ord("0")
+
+    def addStrings(self, num1, num2):
+        """
+        :type num1: str
+        :type num2: str
+        :rtype: str
+        """
+        ret = []
+        # let num2 to be one has more digit
+        if len(num1) > len(num2):
+            num1, num2 = num2, num1
+
+        num1 = num1[::-1]
+        num2 = num2[::-1]
+        carry = 0
+        idx = 0
+        while idx < len(num2):
+            if idx < len(num1):
+                s = self.int(num1[idx]) + self.int(num2[idx]) + carry
+            else:
+                s = self.int(num2[idx]) + carry
+
+            if s >= 10:
+                s -= 10
+                carry = 1
+            else:
+                carry = 0
+
+            ret.append(s)
+            idx += 1
+
+        if carry:
+            ret.append(carry)
+
+        return "".join(map(str, ret[::-1]))
+
+
+if __name__ == "__main__":
+    assert Solution().addStrings("9999", "1") == "10000"
+    assert Solution().addStrings("9999", "9999") == "19998"
+    assert Solution().addStrings("23", "8") == "31"
