Import C# solutions from https://github.com/kfstorm/LeetCode

solution/0001.Two Sum/Solution.cs

@@ -0,0 +1,20 @@
+using System.Collections.Generic;
+
+public class Solution {
+    public int[] TwoSum(int[] nums, int target) {
+        var dict = new Dictionary<int, int>();
+        for (var i = 0; i < nums.Length; ++i)
+        {
+            int index;
+            if (dict.TryGetValue(target - nums[i], out index))
+            {
+                return new [] { index + 1, i + 1};
+            }
+            if (!dict.ContainsKey(nums[i]))
+            {
+                dict.Add(nums[i], i);
+            }
+        }
+        return null;
+    }
+}

solution/0002.Add Two Numbers/Solution.cs

@@ -0,0 +1,26 @@
+public class Solution {
+    public ListNode AddTwoNumbers(ListNode l1, ListNode l2) {
+        return AddInternal(l1, l2, false);
+    }
+
+    private ListNode AddInternal(ListNode l1, ListNode l2, bool plusOne)
+    {
+        if (l1 == null && l2 == null)
+        {
+            if (plusOne)
+            {
+                return new ListNode(1);
+            }
+            return null;
+        }
+
+        var val = (l1 == null ? 0 : l1.val) + (l2 == null ? 0 : l2.val) + (plusOne ? 1 : 0); 
+        plusOne = val >= 10;
+        val %= 10;
+        return new ListNode(val)
+        {
+            //next = AddInternal(l1?.next, l2?.next, plusOne);
+            next = AddInternal(l1 == null ? null : l1.next, l2 == null ? null : l2.next, plusOne)
+        };
+    }
+}

solution/0003.Longest Substring Without Repeating Characters/Solution.cs

@@ -0,0 +1,22 @@
+using System.Collections.Generic;
+
+public class Solution {
+    public int LengthOfLongestSubstring(string s) {
+        var hashSet = new HashSet<char>();
+        var maxLength = 0;
+        int i = 0, j = 0;
+        while (i < s.Length)
+        {
+            while (hashSet.Contains(s[i]))
+            {
+                hashSet.Remove(s[j++]);
+            }
+            hashSet.Add(s[i++]);
+            if (i - j > maxLength)
+            {
+                maxLength = i - j;
+            }
+        }
+        return maxLength;
+    }
+}

solution/0004.Median of Two Sorted Arrays/Solution.cs

@@ -0,0 +1,121 @@
+using System;
+using System.Linq;
+
+class Range
+{
+    public static Range Empty = new Range(new int[0], 0, -1);
+
+    public readonly int[] Numbers;
+    public readonly int LeftIndex;
+    public readonly int RightIndex;
+
+    public int Count { get { return RightIndex - LeftIndex + 1; } }
+
+    public int this[int index]
+    {
+        get
+        {
+            if (index >= Count)
+            {
+                throw new IndexOutOfRangeException();
+            }
+            return Numbers[LeftIndex + index];
+        }
+    }
+
+    public Range(int[] numbers) : this(numbers, 0, numbers.Length - 1)
+    {
+    }
+
+    public Range(int[] numbers, int leftIndex, int rightIndex)
+    {
+        Numbers = numbers;
+        LeftIndex = leftIndex;
+        RightIndex = rightIndex;
+        if (RightIndex < LeftIndex) RightIndex = LeftIndex - 1;
+    }
+
+    public Range GetSubRange(int lowerBound, int upperBound)
+    {
+        if (lowerBound > upperBound) return Empty;
+        var leftIndex = lowerBound == int.MinValue ? LeftIndex : Search(lowerBound);
+        var rightIndex = upperBound == int.MaxValue ? RightIndex : Search(upperBound + 1) - 1;
+        return new Range(Numbers, leftIndex, rightIndex);
+    }
+
+    private int Search(int target)
+    {
+        var l = 0;
+        var r = Numbers.Length - 1;
+        while (l < r)
+        {
+            var mid = (l + r) / 2;
+            if (Numbers[mid] < target)
+            {
+                l = mid + 1;
+            }
+            else
+            {
+                r = mid;
+            }
+        }
+        return Numbers[l] >= target ? l : l + 1;
+    }
+}
+
+public class Solution {
+    public double FindMedianSortedArrays(int[] nums1, int[] nums2)
+    {
+        var totalNumbers = nums1.Length + nums2.Length;
+        var targetOrder1 = (totalNumbers + 1)/2;
+        var targetOrder2 = (totalNumbers + 2)/2;
+        var range1 = new Range(nums1);
+        var range2 = new Range(nums2);
+        var number1 = FindMedianSortedArrays(range1, range2, targetOrder1);
+        var number2 = targetOrder1 == targetOrder2 ? number1 : FindMedianSortedArrays(range1, range2, targetOrder2);
+        return ((double) number1 + number2)/2;
+    }
+
+    private int FindMedianSortedArrays(Range range1, Range range2, int targetOrder)
+    {
+        if (range1.Count == 0)
+        {
+            return range2[targetOrder - 1];
+        }
+        if (range2.Count == 0)
+        {
+            return range1[targetOrder - 1];
+        }
+
+        var midNumber = range1[(range1.Count - 1)/2];
+        var midRanges = new[] { range1.GetSubRange(midNumber, midNumber), range2.GetSubRange(midNumber, midNumber) };
+        var leftRanges = new[]
+        {
+            new Range(range1.Numbers, range1.LeftIndex, midRanges[0].LeftIndex - 1),
+            new Range(range2.Numbers, range2.LeftIndex, midRanges[1].LeftIndex - 1)
+        };
+        var rightRanges = new[]
+        {
+            new Range(range1.Numbers, midRanges[0].RightIndex + 1, range1.RightIndex),
+            new Range(range2.Numbers, midRanges[1].RightIndex + 1, range2.RightIndex)
+        };
+
+        var leftCount = leftRanges.Sum(r => r.Count);
+        var midCount = midRanges.Sum(r => r.Count);
+        var rightCount = rightRanges.Sum(r => r.Count);
+
+        if (leftCount == 0 && rightCount == 0)
+        {
+            return midNumber;
+        }
+        if (leftCount >= targetOrder)
+        {
+            return FindMedianSortedArrays(leftRanges[0], leftRanges[1], targetOrder);
+        }
+        if (leftCount + midCount >= targetOrder)
+        {
+            return FindMedianSortedArrays(midRanges[0], midRanges[1], targetOrder - leftCount);
+        }
+        return FindMedianSortedArrays(rightRanges[0], rightRanges[1], targetOrder - leftCount - midCount);
+    }
+}

solution/0005.Longest Palindromic Substring/Solution.cs

@@ -0,0 +1,31 @@
+public class Solution {
+    public string LongestPalindrome(string s) {
+        var f = new bool[s.Length];
+        var maxLen = 0;
+        var index = 0;
+        for (var p = 0; p <= 1; ++p)
+        {
+            for (var l = 1 + p; l <= s.Length; l += 2)
+            {
+                for (var i = 0; i <= s.Length - l; ++i)
+                {
+                    if (l <= 2)
+                    {
+                        f[i] = s[i] == s[i + l - 1]; 
+                    }
+                    else
+                    {
+                        f[i] = f[i + 1] && s[i] == s[i + l - 1]; 
+                    }
+                    if (f[i] && l > maxLen)
+                    {
+                        maxLen = l;
+                        index = i;
+                    }
+                }
+            }
+        }
+
+        return s.Substring(index, maxLen);
+    }
+}

solution/0006.ZigZag Conversion/Solution.cs

@@ -0,0 +1,29 @@
+using System.Collections.Generic;
+using System.Linq;
+
+public class Solution {
+    public string Convert(string s, int numRows) {
+        if (numRows == 1) return s;
+        if (numRows > s.Length) numRows = s.Length;
+        var rows = new List<char>[numRows];
+        var i = 0;
+        var j = 0;
+        var down = true;
+        while (i < s.Length)
+        {
+            if (rows[j] == null)
+            {
+                rows[j] = new List<char>();
+            }
+            rows[j].Add(s[i]);
+            j = j + (down ? 1 : -1);
+            if (j == numRows || j < 0)
+            {
+                down = !down;
+                j = j + (down ? 2 : -2);
+            }
+            ++i;
+        }
+        return new string(rows.SelectMany(row => row).ToArray());
+    }
+}

solution/0007.Reverse Integer/Solution.cs

@@ -0,0 +1,15 @@
+public class Solution {
+    public int Reverse(int x) {
+        var negative = x < 0;
+        if (negative) x = -x;
+        long result = 0;
+        while (x > 0)
+        {
+            result = (result * 10) + x % 10;
+            x /= 10;
+        }
+        if (negative) result = -result;
+        if (result > int.MaxValue || result < int.MinValue) result = 0;
+        return (int) result;
+    }
+}

solution/0008.String to Integer (atoi)/Solution.cs

@@ -0,0 +1,46 @@
+// https://leetcode.com/problems/string-to-integer-atoi/
+
+public partial class Solution
+{
+    public int MyAtoi(string str)
+    {
+        int i = 0;
+        long result = 0;
+        bool minus = false;
+        while (i < str.Length && char.IsWhiteSpace(str[i]))
+        {
+            ++i;
+        }
+        if (i < str.Length)
+        {
+            if (str[i] == '+')
+            {
+                ++i;
+            }
+            else if (str[i] == '-')
+            {
+                minus = true;
+                ++i;
+            }
+        }
+        while (i < str.Length && char.IsDigit(str[i]))
+        {
+            result = result * 10 + str[i] - '0';
+            if (result > int.MaxValue)
+            {
+                break;
+            }
+            ++i;
+        }
+        if (minus) result = -result;
+        if (result > int.MaxValue)
+        {
+            result = int.MaxValue;
+        }
+        if (result < int.MinValue)
+        {
+            result = int.MinValue;
+        }
+        return (int)result;
+    }
+}

solution/0010.Regular Expression Matching/Solution.cs

@@ -0,0 +1,47 @@
+public class Solution {
+    public bool IsMatch(string s, string p) {
+        var f = new bool[s.Length + 1, p.Length + 1];
+        f[0, 0] = true;
+        for (var i = 0; i <= s.Length; ++i)
+        {
+            for (var j = 0; j <= p.Length; ++j)
+            {
+                if (i != 0 || j != 0)
+                {
+                    if (j == 0)
+                    {
+                        f[i, j] = false;
+                    }
+                    else if (i == 0)
+                    {
+                        if (p[j - 1] == '*')
+                        {
+                            f[i, j] = f[i, j - 2];
+                        }
+                        else
+                        {
+                            f[i, j] = false;
+                        }
+                    }
+                    else
+                    {
+                        if (p[j - 1] == '.')
+                        {
+                            f[i, j] = f[i - 1, j - 1];
+                        }
+                        else if (p[j - 1] == '*')
+                        {
+                            f[i, j] = f[i - 1, j] && (s[i - 1] == p[j - 2] || p[j - 2] == '.') || f[i, j - 2];
+                        }
+                        else
+                        {
+                            f[i, j] = f[i - 1, j - 1] && s[i - 1] == p[j - 1];
+                        }
+                    }
+                }
+            }
+        }
+
+        return f[s.Length, p.Length];
+    }
+}

solution/0014.Longest Common Prefix/Solution.cs

@@ -0,0 +1,22 @@
+using System.Text;
+using System.Linq;
+
+public class Solution {
+    public string LongestCommonPrefix(string[] strs) {
+        if (strs.Length == 0) return string.Empty;
+        var sb = new StringBuilder();
+        for (var i = 0; i < strs[0].Length; ++i)
+        {
+            var ch = strs[0][i];
+            if (strs.All(str => str.Length > i && str[i] == ch))
+            {
+                sb.Append(ch);
+            }
+            else
+            {
+                break;
+            }
+        }
+        return sb.ToString();
+    }
+}