Merge pull request youngyangyang04#1310 from UndeadSheep/master

新增 哈希表部分的 C#版

Author: youngyangyang04

problems/0001.两数之和.md

@@ -274,6 +274,24 @@ class Solution {
     }
 }
 ```
+C#:
+```csharp
+public class Solution {
+    public int[] TwoSum(int[] nums, int target) {
+        Dictionary<int ,int> dic= new Dictionary<int,int>();
+        for(int i=0;i<nums.Length;i++){
+            int imp= target-nums[i];
+            if(dic.ContainsKey(imp)&&dic[imp]!=i){
+               return new int[]{i, dic[imp]};
+            }
+            if(!dic.ContainsKey(nums[i])){
+                dic.Add(nums[i],i);
+            }
+        }
+        return new int[]{0, 0};
+    }
+}
+```
 
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0202.快乐数.md

@@ -385,5 +385,28 @@ bool isHappy(int n){
     return bHappy;
 }
 ```
+
+C#：
+```csharp
+public class Solution {
+    private int getSum(int n) {
+        int sum = 0;
+        //每位数的换算
+        while (n > 0) {
+            sum += (n % 10) * (n % 10);
+            n /= 10;
+        }
+        return sum;
+    }
+    public bool IsHappy(int n) {
+        HashSet <int> set = new HashSet<int>();
+        while(n != 1 && !set.Contains(n)) { //判断避免循环
+            set.Add(n);
+            n = getSum(n);
+        }
+        return n == 1;
+    }
+}
+```
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0242.有效的字母异位词.md

@@ -307,6 +307,25 @@ impl Solution {
     }
 }
 ```
+
+C#：
+```csharp
+ public bool IsAnagram(string s, string t) {
+         int sl=s.Length,tl=t.Length;
+        if(sl!=tl) return false;
+        int[] a = new int[26];
+        for(int i = 0; i < sl; i++){
+             a[s[i] - 'a']++;
+             a[t[i] - 'a']--;
+        }       
+        foreach (int i in a)
+        {
+            if (i != 0)
+                return false;
+        }
+        return true;
+    }
+```
 ## 相关题目
 
 * 383.赎金信

problems/0349.两个数组的交集.md

@@ -313,6 +313,24 @@ int* intersection1(int* nums1, int nums1Size, int* nums2, int nums2Size, int* re
 }
 ```
 
+C#:
+```csharp
+ public int[] Intersection(int[] nums1, int[] nums2) {
+    if(nums1==null||nums1.Length==0||nums2==null||nums1.Length==0)
+    	return new int[0]; //注意数组条件
+    HashSet<int> one = Insert(nums1);
+    HashSet<int> two = Insert(nums2);
+    one.IntersectWith(two);
+    return one.ToArray();
+	}
+ public HashSet<int> Insert(int[] nums){
+    HashSet<int> one = new HashSet<int>();
+    foreach(int num in nums){
+    	one.Add(num);         
+    	}
+        return one;
+	}
+```
 ## 相关题目
 
 * 350.两个数组的交集 II

problems/0383.赎金信.md

@@ -363,5 +363,22 @@ impl Solution {
 }
 ```
 
+C#：
+```csharp
+public bool CanConstruct(string ransomNote, string magazine) {
+        if(ransomNote.Length > magazine.Length) return false;
+        int[] letters = new int[26]; 
+        foreach(char c in magazine){
+            letters[c-'a']++;
+        }
+        foreach(char c in ransomNote){
+            letters[c-'a']--;
+            if(letters[c-'a']<0){
+                return false;
+            }
+        }
+        return true;
+    }
+```
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>

problems/0454.四数相加II.md

@@ -318,5 +318,32 @@ impl Solution {
 }
 ```
 
+C#：
+```csharp
+public int FourSumCount(int[] nums1, int[] nums2, int[] nums3, int[] nums4) {
+       Dictionary<int, int> dic = new Dictionary<int, int>();
+        foreach(var i in nums1){
+            foreach(var j in nums2){
+                int sum = i + j;
+                if(dic.ContainsKey(sum)){
+                    dic[sum]++;
+                }else{
+                    dic.Add(sum, 1);
+                }
+                
+            }
+        }
+        int res = 0;
+         foreach(var a in nums3){
+            foreach(var b in nums4){
+                int sum = a+b;
+                if(dic.TryGetValue(-sum, out var result)){
+                    res += result;
+                }
+            }
+        }
+        return res;
+    }
+```
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 <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img></div>