Merge pull request #2330 from eeee0717/master

Update 028.实现strStr，添加C#版本

problems/0024.两两交换链表中的节点.md

@@ -459,6 +459,40 @@ impl Solution {
 }
 ```
 
+### C#
+```C#
+// 虚拟头结点
+public ListNode SwapPairs(ListNode head)
+{
+    var dummyHead = new ListNode();
+    dummyHead.next = head;
+    ListNode cur = dummyHead;
+    while (cur.next != null && cur.next.next != null)
+    {
+        ListNode tmp1 = cur.next;
+        ListNode tmp2 = cur.next.next.next;
+
+        cur.next = cur.next.next;
+        cur.next.next = tmp1;
+        cur.next.next.next = tmp2;
+
+        cur = cur.next.next;
+    }
+    return dummyHead.next;
+}
+```
+``` C#
+// 递归
+public ListNode SwapPairs(ListNode head)
+{
+    if (head == null || head.next == null) return head;
+    var cur = head.next;
+    head.next = SwapPairs(head.next.next);
+    cur.next = head;
+    return cur;
+}
+```
+
 <p align="center">
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">
   <img src="../pics/网站星球宣传海报.jpg" width="1000"/>

problems/0028.实现strStr.md

@@ -1358,6 +1358,72 @@ impl Solution {
 }
 ```
 
+>前缀表统一不减一
+```C#
+public int StrStr(string haystack, string needle)
+{
+    if (string.IsNullOrEmpty(needle))
+        return 0;
+
+    if (needle.Length > haystack.Length || string.IsNullOrEmpty(haystack))
+        return -1;
+
+    return KMP(haystack, needle);
+}
+
+public int KMP(string haystack, string needle)
+{
+    int[] next = GetNext(needle);
+    int i = 0, j = 0;
+    while (i < haystack.Length)
+    {
+        if (haystack[i] == needle[j])
+        {
+            i++;
+            j++;
+        }
+        if (j == needle.Length)
+            return i-j;
+        else if (i < haystack.Length && haystack[i] != needle[j])
+            if (j != 0)
+            {
+                j = next[j - 1];
+            }
+            else
+            {
+                i++;
+            }
+    }
+    return -1;
+}
+
+public int[] GetNext(string needle)
+{
+    int[] next = new int[needle.Length];
+    next[0] = 0;
+    int i = 1, j = 0;
+    while (i < needle.Length)
+    {
+        if (needle[i] == needle[j])
+        {
+            next[i++] = ++j;
+        }
+        else
+        {
+            if (j == 0)
+            {
+                next[i++] = 0;
+            }
+            else
+            {
+                j = next[j - 1];
+            }
+        }
+    }
+    return next;
+}
+```
+
 <p align="center">
 <a href="https://programmercarl.com/other/kstar.html" target="_blank">
   <img src="../pics/网站星球宣传海报.jpg" width="1000"/>

problems/0151.翻转字符串里的单词.md

@@ -972,6 +972,13 @@ char * reverseWords(char * s){
 }
 ```
 
+### C#
+```C# LINQ高级方法
+public string ReverseWords(string s) {
+    return string.Join(' ', s.Trim().Split(' ',StringSplitOptions.RemoveEmptyEntries).Reverse());
+}
+```
+
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problems/0459.重复的子字符串.md

@@ -681,6 +681,32 @@ impl Solution {
     }
 }
 ```
+### C#
+```C#
+// 前缀表不减一
+public bool RepeatedSubstringPattern(string s)
+{
+    if (s.Length == 0)
+        return false;
+    int[] next = GetNext(s);
+    int len = s.Length;
+    if (next[len - 1] != 0 && len % (len - next[len - 1]) == 0) return true;
+    return false;
+}
+public int[] GetNext(string s)
+{
+    int[] next = Enumerable.Repeat(0, s.Length).ToArray();
+    for (int i = 1, j = 0; i < s.Length; i++)
+    {
+        while (j > 0 && s[i] != s[j])
+            j = next[j - 1];
+        if (s[i] == s[j])
+            j++;
+        next[i] = j;
+    }
+    return next;
+}
+```
 
 
 <p align="center">

problems/0707.设计链表.md

@@ -1485,6 +1485,77 @@ impl MyLinkedList {
 }
 ```
 
+### C#
+```C#
+class ListNode
+{
+    public int val;
+    public ListNode next;
+    public ListNode(int val) { this.val = val; }
+}
+public class MyLinkedList
+{
+    ListNode dummyHead;
+    int count;
+
+    public MyLinkedList()
+    {
+        dummyHead = new ListNode(0);
+        count = 0;
+    }
+
+    public int Get(int index)
+    {
+        if (index < 0 || count <= index) return -1;
+        ListNode current = dummyHead;
+        for (int i = 0; i <= index; i++)
+        {
+            current = current.next;
+        }
+        return current.val;
+    }
+
+    public void AddAtHead(int val)
+    {
+        AddAtIndex(0, val);
+    }
+
+    public void AddAtTail(int val)
+    {
+        AddAtIndex(count, val);
+    }
+
+    public void AddAtIndex(int index, int val)
+    {
+        if (index > count) return;
+        index = Math.Max(0, index);
+        count++;
+        ListNode tmp1 = dummyHead;
+        for (int i = 0; i < index; i++)
+        {
+            tmp1 = tmp1.next;
+        }
+        ListNode tmp2 = new ListNode(val);
+        tmp2.next = tmp1.next;
+        tmp1.next = tmp2;
+    }
+
+    public void DeleteAtIndex(int index)
+    {
+
+        if (index >= count || index < 0) return;
+        var tmp1 = dummyHead;
+        for (int i = 0; i < index; i++)
+        {
+            tmp1 = tmp1.next;
+        }
+        tmp1.next = tmp1.next.next;
+        count--;
+
+    }
+}
+```
+
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problems/面试题02.07.链表相交.md

@@ -502,6 +502,20 @@ object Solution {
   }
 }
 ```
+### C#
+```C#
+public ListNode GetIntersectionNode(ListNode headA, ListNode headB)
+{
+    if (headA == null || headB == null) return null;
+    ListNode cur1 = headA, cur2 = headB;
+    while (cur1 != cur2)
+    {
+        cur1 = cur1 == null ? headB : cur1.next;
+        cur2 = cur2 == null ? headA : cur2.next;
+    }
+    return cur1;
+}
+```
 
 
 <p align="center">