array to treenode extension method

Author: codeyu

Algorithms/Utils/Helper.cs

@@ -7,11 +7,11 @@ public static class Helper
     {
         public static ListNode<int> ToListNode(this List<int> lst)
         {
-            if(lst.Count>0 && lst.Where(x=>x>=10).Count()==0)
+            if (lst.Count > 0 && lst.Where(x => x >= 10).Count() == 0)
             {
                 ListNode<int> head = new ListNode<int>(lst[0]);
                 ListNode<int> current = head;
-                for (var i=1;i<lst.Count;i++)
+                for (var i = 1; i < lst.Count; i++)
                 {
                     current.Next = new ListNode<int>(lst[i]);
                     current = current.Next;
@@ -22,12 +22,20 @@ public static ListNode<int> ToListNode(this List<int> lst)
         }
         public static TreeNode ToTreeNode(this int?[] arr)
         {
-            throw new NotImplementedException("TODO");
+            return ToTreeNode(arr, 0, arr.Length);
+        }
+        private static TreeNode ToTreeNode(int?[] arr, int i, int n)
+        {
+            if (i >= n || arr[i] == null) return null;
+            TreeNode tn = new TreeNode(arr[i].Value);
+            tn.Left = ToTreeNode(arr, 2 * i + 1, n);
+            tn.Right = ToTreeNode(arr, 2 * i + 2, n);
+            return tn;
         }
         public static List<int> ToList(this ListNode<int> node)
         {
             var lst = new List<int>();
-            while(node != null)
+            while (node != null)
             {
                 lst.Add(node.Val);
                 node = node.Next;
@@ -36,33 +44,33 @@ public static List<int> ToList(this ListNode<int> node)
         }
         public static void BubbleSort(int[] nums)
         {
-            for(int i = 0; i < nums.Length - 1; i++)
+            for (int i = 0; i < nums.Length - 1; i++)
             {
-                for(int j=0; j< nums.Length - 1 - i; j++)
+                for (int j = 0; j < nums.Length - 1 - i; j++)
                 {
-                    if(nums[j] > nums[j+1])
+                    if (nums[j] > nums[j + 1])
                     {
                         int tmp = nums[j];
-                        nums[j] = nums[j+1];
-                        nums[j+1] = tmp;
+                        nums[j] = nums[j + 1];
+                        nums[j + 1] = tmp;
                     }
                 }
             }
         }
         public static void BubbleSort2(int[] nums)
         {
             int i = nums.Length - 1;
-            while(i > 0)
+            while (i > 0)
             {
                 int pos = 0;
-                for(int j = 0; j < i; j++)
+                for (int j = 0; j < i; j++)
                 {
-                    if(nums[j] > nums[j+1])
+                    if (nums[j] > nums[j + 1])
                     {
                         pos = j;//记录交换的位置
                         int tmp = nums[j];
-                        nums[j] = nums[j+1];
-                        nums[j+1] = tmp;
+                        nums[j] = nums[j + 1];
+                        nums[j + 1] = tmp;
                     }
                 }
                 i = pos;
@@ -73,25 +81,25 @@ public static void BubbleSort3(int[] nums)
             int low = 0;
             int high = nums.Length - 1;
             int tmp, j;
-            while(low < high)
+            while (low < high)
             {
-                for(j=low; j<high;j++)
+                for (j = low; j < high; j++)
                 {
-                    if(nums[j] > nums[j+1])
+                    if (nums[j] > nums[j + 1])
                     {
                         tmp = nums[j];
-                        nums[j] = nums[j+1];
-                        nums[j+1] = tmp;
+                        nums[j] = nums[j + 1];
+                        nums[j + 1] = tmp;
                     }
                 }
                 high--;
-                for(j=high;j>low;j--)
+                for (j = high; j > low; j--)
                 {
-                    if(nums[j] < nums[j-1])
+                    if (nums[j] < nums[j - 1])
                     {
                         tmp = nums[j];
-                        nums[j] = nums[j-1];
-                        nums[j-1] = tmp;
+                        nums[j] = nums[j - 1];
+                        nums[j - 1] = tmp;
                     }
                 }
                 low++;
@@ -101,68 +109,68 @@ public static void Sort(int[] arr)
         {
             SortMerge(arr, 0, arr.Length - 1);
         }
-         static void MainMerge(int[] numbers, int left, int mid, int right)
+        static void MainMerge(int[] numbers, int left, int mid, int right)
         {
             int[] temp = new int[numbers.Length];
             int i, eol, num, pos;
- 
+
             eol = (mid - 1);
             pos = left;
             num = (right - left + 1);
- 
+
             while ((left <= eol) && (mid <= right))
             {
                 if (numbers[left] <= numbers[mid])
                     temp[pos++] = numbers[left++];
                 else
                     temp[pos++] = numbers[mid++];
             }
- 
+
             while (left <= eol)
                 temp[pos++] = numbers[left++];
- 
+
             while (mid <= right)
                 temp[pos++] = numbers[mid++];
- 
+
             for (i = 0; i < num; i++)
             {
                 numbers[right] = temp[right];
                 right--;
             }
         }
- 
+
         static void SortMerge(int[] numbers, int left, int right)
         {
             int mid;
- 
+
             if (right > left)
             {
                 mid = (right + left) / 2;
                 SortMerge(numbers, left, mid);
                 SortMerge(numbers, (mid + 1), right);
- 
+
                 MainMerge(numbers, left, (mid + 1), right);
             }
         }
 
         public static void QuickSort(int[] nums)
         {
-            QuickSort(nums, 0 , nums.Length - 1);
+            QuickSort(nums, 0, nums.Length - 1);
         }
         private static void QuickSort(int[] nums, int low, int high)
         {
-            int privotLoc = Partition(nums,low,high);
-            QuickSort(nums,low,privotLoc - 1);
+            int privotLoc = Partition(nums, low, high);
+            QuickSort(nums, low, privotLoc - 1);
             QuickSort(nums, privotLoc + 1, high);
         }
         private static int Partition(int[] a, int low, int high)
         {
             int privotKey = a[low];
-            while(low < high)
+            while (low < high)
             {
-                while(low < high && a[high] >= privotKey){ high--; }
+                while (low < high && a[high] >= privotKey) { high--; }
                 Swap(a[low], a[high]);
-                while(low < high && a[low] <= privotKey){ low++; }
+                while (low < high && a[low] <= privotKey) { low++; }
                 Swap(a[low], a[high]);
             }
             return low;