change on atoi

Author: v-lili

Algorithms Basics/Chapter 1. Array_String/8. String to Integer (atoi).cs

@@ -8,38 +8,35 @@ 2. takes an optional '+' or '-'
         5. If out of int range, return INT_MAX(2147483647) or INT_MIN(-2147483648)
         */
 
+    private static readonly int maxDiv10 = int.MaxValue / 10;
     public int MyAtoi(string str)
     {
         if (str == null) return 0;
-        str = str.Trim();
-        if (str.Length == 0) return 0;
+        int i = 0, n = str.Length;
+        while (i < n && char.IsWhiteSpace(str[i])) i++;
+        if (i == n) return 0;
         int sign = 1;
-        int index = 0;
-        if (str[index] == '+') index++;
-        else if (str[index] == '-') {
+        if (i < n && str[i] == '+') {
+            i++;
+        } else if (i < n && str[i] == '-') {
             sign = -1;
-            index++;
+            i++;
         }
-        long num = 0;
-        for (; index < str.Length; index++) {
-            if (str[index] < '0' || str[index] > '9')
-            {
-                break;
+        int num = 0;
+        while (i < n && char.IsDigit(str[i])) {
+            int digit = str[i] - '0';
+            if (num > maxDiv10 || num == maxDiv10 && digit >= 8) {
+                return sign == 1 ? int.MaxValue : int.MinValue;
             }
-            num = num * 10 + str[index] - '0';
-            if (num > int.MaxValue)
-            {
-                break;
-            }
-        }
-        if (num * sign >= int.MaxValue)
-        {
-            return int.MaxValue;
-        } 
-        if (num * sign <= int.MinValue)
-        {
-            return int.MinValue;
+            num = num * 10 + digit;
+            i++;
         }
-        return (int)num * sign;
+        return sign * num;
     }
-}
+}
+
+/*
+Next challenges: 
+Reverse Integer
+Valid Number
+ */

CodeClearWar/8. String to Integer (atoi).cs

@@ -0,0 +1,42 @@
+public class Solution {
+    /*
+        Requirements for atoi:
+        1. trim whitespace
+        2. takes an optional '+' or '-'
+        3. when meet non-numetic char, break " - 0012a43" return -12
+        4. If no valid conversion could be performed, 0 is returned.
+        5. If out of int range, return INT_MAX(2147483647) or INT_MIN(-2147483648)
+        */
+
+    private static readonly int maxDiv10 = int.MaxValue / 10;
+    public int MyAtoi(string str)
+    {
+        if (str == null) return 0;
+        int i = 0, n = str.Length;
+        while (i < n && char.IsWhiteSpace(str[i])) i++;
+        if (i == n) return 0;
+        int sign = 1;
+        if (i < n && str[i] == '+') {
+            i++;
+        } else if (i < n && str[i] == '-') {
+            sign = -1;
+            i++;
+        }
+        int num = 0;
+        while (i < n && char.IsDigit(str[i])) {
+            int digit = str[i] - '0';
+            if (num > maxDiv10 || num == maxDiv10 && digit >= 8) {
+                return sign == 1 ? int.MaxValue : int.MinValue;
+            }
+            num = num * 10 + digit;
+            i++;
+        }
+        return sign * num;
+    }
+}
+
+/*
+Next challenges: 
+Reverse Integer
+Valid Number
+ */

LeetcodeCShaprDotNetCore/Program.cs

@@ -3,8 +3,8 @@
 namespace LeetcodeCShaprDotNetCore {
     class Program {
         static void Main(string[] args) {
-            var s = new int[]{ 1, 0, -1, 0, -2, 2 };
-            var res = Solution.FourSum(s, 0);
+            var s = "1";
+            int i = Solution.MyAtoi(s);
             Console.ReadLine();
         }
 

LeetcodeCShaprDotNetCore/Solution.cs

@@ -4,32 +4,35 @@
 
 namespace LeetcodeCShaprDotNetCore
 {
+
     public class Solution
     {
-        public ListNode RotateRight(ListNode head, int k)
+        private static readonly int maxDiv10 = int.MaxValue / 10;
+        public static int MyAtoi(string str)
         {
-            if (head == null || head.next == null) return head;
-            // get length
-            int len = 1;
-            ListNode tail = head;
-            while (tail.next != null)
+            int i = 0, n = str.Length;
+            while (i < n && char.IsWhiteSpace(str[i])) i++;
+            int sign = 1;
+            if (i < n && str[i] == '+') {
+                i++;
+            }
+            else if (i < n && str[i] == '-')
             {
-                tail = tail.next;
-                len++;
+                sign = -1;
+                i++;
             }
-            // connect circle
-            tail.next = head;
-            // find new head;
-            var n = len - k % len;
-            while (n > 0)
+            int num = 0;
+            while (i < n && char.IsDigit(str[i]))
             {
-                tail = head;
-                head = head.next;
-                n--;
+                int digit = str[i] - '0';
+                if (num > maxDiv10 || num == maxDiv10 && digit >= 8)
+                {
+                    return sign == 1 ? int.MaxValue : int.MinValue;
+                }
+                num = num * 10 + digit;
+                i++;
             }
-            // cut before the new head
-            tail.next = null;
-            return head;
+            return sign * num;
         }
     }
 }