re-arrange folder and files

Author: Li Li

Algorithms Basics/Chapter 1. Array_String/167. Two Sum II - Input array is sorted/similar problem/1. Two Sum.cs renamed to Algorithms Basics/Chapter 1. Array_String/1. Two Sum.cs

@@ -1,4 +1,9 @@
-public class Solution {
+/*
+Similar problems:
+1. Two Sum
+653. Two Sum IV - Input is a BST
+ */
+public class Solution {
     public int[] TwoSum(int[] nums, int target) {
         int[] res = null;
         if (nums == null || nums.Length == 0) {

Algorithms Basics/Chapter 1. Array_String/167. Two Sum II - Input array is sorted/167. Two Sum II - Input array is sorted.cs renamed to Algorithms Basics/Chapter 1. Array_String/167. Two Sum II - Input array is sorted.cs

@@ -1,3 +1,7 @@
+/*
+Similar problems:
+438. Find All Anagrams in a String
+ */
 public class Solution {
     public bool IsAnagram(string s, string t) {
         if (s == null) return t == null;

Algorithms Basics/Chapter 1. Array_String/26. Remove Duplicates from Sorted Array/similar problems/203. Remove Linked List Elements.cs renamed to Algorithms Basics/Chapter 1. Array_String/203. Remove Linked List Elements.cs

@@ -1,4 +1,10 @@
-class Solution
+/*
+Similar problems:
+27. Remove Element; 
+203. Remove Linked List Elements; 
+283. Move Zeroes;
+ */
+class Solution
 {
     public int RemoveDuplicates(int[] nums)
     {

Algorithms Basics/Chapter 1. Array_String/242. Valid Anagram/242. Valid Anagram.cs renamed to Algorithms Basics/Chapter 1. Array_String/242. Valid Anagram.cs

@@ -1,3 +1,7 @@
+/*
+Similar Problem:
+459. Repeated Substring Pattern
+ */
 public class Solution {
     public int StrStr(string haystack, string needle) {
         if (haystack == null || needle == null) {

Algorithms Basics/Chapter 1. Array_String/26. Remove Duplicates from Sorted Array/26. Remove Duplicates from Sorted Array.cs renamed to Algorithms Basics/Chapter 1. Array_String/26. Remove Duplicates from Sorted Array.cs

@@ -0,0 +1,45 @@
+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)
+        */
+
+    public int MyAtoi(string str)
+    {
+        if (str == null) return 0;
+        str = str.Trim();
+        if (str.Length == 0) return 0;
+        int sign = 1;
+        int index = 0;
+        if (str[index] == '+') index++;
+        else if (str[index] == '-') {
+            sign = -1;
+            index++;
+        }
+        long num = 0;
+        for (; index < str.Length; index++) {
+            if (str[index] < '0' || str[index] > '9')
+            {
+                break;
+            }
+            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;
+        }
+        return (int)num * sign;
+    }
+}

Algorithms Basics/Chapter 1. Array_String/26. Remove Duplicates from Sorted Array/similar problems/27. Remove Element.cs renamed to Algorithms Basics/Chapter 1. Array_String/27. Remove Element.cs

@@ -1,17 +1,25 @@
 using System;
-
+using System.Collections.Generic;
 namespace LeetcodeCShaprDotNetCore {
     class Program {
         static void Main(string[] args) {
-            var s = new Solution();
-            var r = s.TwoSum(new int[] { 11, 7, 2, 15 }, 9);
-            System.Console.WriteLine(r[0] + " " + r[1]);
+            var solution = new Solution2();
+            var s1 = "abab";
+            var s2 = "aba";
+            var s3 = "abcabcabcabc";
+            System.Console.WriteLine(solution.RepeatedSubstringPattern(s1));
+            System.Console.WriteLine(solution.RepeatedSubstringPattern(s2));
+            System.Console.WriteLine(solution.RepeatedSubstringPattern(s3));
         }
     }
 }
 
 
 /*
-Input: numbers={2, 7, 11, 15}, target=9
-Output: index1=1, index2=
-*/
+Given "abcabcbb", the answer is "abc", which the length is 3.
+
+Given "bbbbb", the answer is "b", with the length of 1.
+
+Given "pwwkew", the answer is "wke", with the length of 3. 
+Note that the answer must be a substring, "pwke" is a subsequence and not a substring.
+ */

Algorithms Basics/Chapter 1. Array_String/28. Implement strStr()/28. Implement strStr().cs renamed to Algorithms Basics/Chapter 1. Array_String/28. Implement strStr().cs

@@ -4,29 +4,48 @@
 
 namespace LeetcodeCShaprDotNetCore {
     public class Solution {
-        public bool IsAnagram(string s, string t) {
-            if (s == null) return t == null;
-            if (t == null) return false;
-            int m = s.Length, n = t.Length;
-            if (m != n) return false;
-            var dict = new Dictionary<char, int>();
-            for (var i = 0; i < m; i++) {
-                if (!dict.ContainsKey(s[i])) {
-                    dict[s[i]] = 1;
-                } else {
-                    dict[s[i]]++;
-                }
+        /*
+            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)
+         */
+
+        public int MyAtoi(string str)
+        {
+            if (str == null) return 0;
+            str = str.Trim();
+            if (str.Length == 0) return 0;
+            int sign = 1;
+            int index = 0;
+            if (str[index] == '+') index++;
+            else if (str[index] == '-') {
+                sign = -1;
+                index++;
             }
-            for (var i = 0; i < n; i++) {
-                if (!dict.ContainsKey(t[i])) {
-                    return false;
+            long num = 0;
+            for (; index < str.Length; index++) {
+                if (str[index] < '0' || str[index] > '9')
+                {
+                    break;
                 }
-                dict[t[i]]--;
-                if (dict[t[i]] < 0) {
-                    return false;
+                num = num * 10 + str[index] - '0';
+                if (num > int.MaxValue)
+                {
+                    break;
                 }
             }
-            return true;
+            if (num * sign >= int.MaxValue)
+            {
+                return int.MaxValue;
+            } 
+            if (num * sign <= int.MinValue)
+            {
+                return int.MinValue;
+            }
+            return (int)num * sign;
         }
     }
 }

Algorithms Basics/Chapter 1. Array_String/26. Remove Duplicates from Sorted Array/similar problems/283. Move Zeroes.cs renamed to Algorithms Basics/Chapter 1. Array_String/283. Move Zeroes.cs

@@ -2,7 +2,13 @@
 
 I will use this repository to make notes for leetcode solutions and sort similar questions into the same group or category.
 
-### Solved Problem (8)
+### Solved Problem List
+
+## Algorithms Basics
+
+First, I will start from the very basic and useful part. The Leetcode Course Section, which is selected interview questions aimed for beginners who do not know algorithms or need a refresher. Learn by doing.
+
+### Chapter 1. Array / String (with similar problem)
 
 ID | Difficulty | Tags | Solution
 -- | ---------- | ---- | --------
@@ -22,82 +28,3 @@ ID | Difficulty | Tags | Solution
 <br />
 <br />
 
-## Algorithms Basics
-
-First, I will start from the very basic and useful part. The Leetcode Course Section, which is selected interview questions aimed for beginners who do not know algorithms or need a refresher. Learn by doing.
-
-### Chapter 1. Array / String
-
-#### 26. Remove Duplicates from Sorted Array
-
-This problem can be solved by typical double pointer technique.
-
-**Algorithm**
-Since the array is already sorted, we can keep two pointers *slow* and *fast*. As long as nums[*fast*] = nums[*slow*], we increse *fast* to skip the duplicate.
-
-When we encounter nums[*fast*] != nums[*slow*], the duplicate run has ended so we must copy its value to nums[*slow* + 1]. ii is then incremented and we repeat the same process again until *fast* reaches the end of array.
-The core part for the solution code is as below:
-
-```csharp
-class Solution
-{
-    public int RemoveDuplicates(int[] nums)
-    {
-        if (nums == null || nums.Length == 0)
-        {
-            return 0;
-        }
-        int slow = 0;
-        for (int fast = 0; fast < nums.Length; fast++)
-        {
-            if (nums[fast] != nums[slow])
-            {
-                nums[++slow] = nums[fast];
-            }
-        }
-        return slow + 1;
-    }
-}
-```
-
-Similar problems:
-
-*27.* Remove Element; 
-*203.* Remove Linked List Elements; 
-*283.* Move Zeroes (error prone, double think for more cases)
-
-#### 167. Two Sum II - Input array is sorted
-
-This problem can be solved by typical double pointer technique.
-
-**Algorithm**
-Since the array is already sorted, we can keep two pointers *left* and *right*. let v = nums[*left*] + nums[*right*], if v < target, left++; if v > target, right--; if v == target, then return.
-
-Similar problems:
-*1.* Two Sum (use dict for each item just use almost O(1) check time, so totally O(n) time);
-*653.* Two Sum IV - Input is a BST (3 solution to revisit) 
-
-#### 242. Valid Anagram
-
-This problem can be solved by using Dictionary.
-
-**Algorithm**
-First use dict record the counts for each char in string1, then check for string2, for each char c, if !dict.ContainsKey(c), return fasle; else dict[c]--, if dict[c] < 0, return false.
-
-Similar problems:
-*438.* Find All Anagrams in a String (using sliding window in substring)
-
-#### 3. Longest Substring Without Repeating Characters
-
-This problem can be solved by using Dictionary, Two pointers.
-Error prone. Think more about different cases.
-
-**Algorithm**
-Use dict save record for char. Use two pointers as a sliding window for substring problem. If the char at right pointer exists in the dict, just move the left pointer to skip the same previous char (be careful to compare if left pointer is already larger than the previous char index).
-
-#### 28. Implement strStr()
-
-This problem can be solve either by brute force or using hash method or KMP.
-
-Similar Problem:
-*459.* Repeated Substring Pattern