leetcode: atoi

Author: shangchun

atoi.py

@@ -0,0 +1,39 @@
+# @return an integer
+def atoi(s):
+        n = 0
+        sign = 1
+        prev = ''
+        for i in s:
+            if prev == '' or prev == ' ':
+                if i == '+':
+                    sign = 1
+                elif i == '-':
+                    sign = -1
+                elif i >= '0' and i <= '9':
+                    n = n * 10 + ord(i) - ord('0')
+                elif i != ' ':
+                    return 0
+            elif prev == '+' or prev == '-' or (prev >= '0' and prev <= '9'):
+                if i < '0' or i > '9':
+                    break;
+                n = n * 10 + ord(i) - ord('0')
+                if n * sign > 2147483647:
+                    return 2147483647
+                elif n * sign < -2147483648:
+                    return -2147483648
+            prev = i
+        return n * sign
+
+
+assert atoi('123') == 123
+assert atoi('-123') == -123
+assert atoi('0123') == 123
+assert atoi('-0123') == -123
+assert atoi(' 123') == 123
+assert atoi(' -123') == -123
+assert atoi(' 123abc') == 123
+assert atoi('2147483648') == 2147483647
+assert atoi('-2147483649') == -2147483648
+assert atoi('+-123') == 0
+assert atoi('- 123') == 0
+assert atoi('   +0 123') == 0