new soln

Author: shreymehul

153.FindMin.cs

@@ -0,0 +1,36 @@
+// 153. Find Minimum in Rotated Sorted Array
+// Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example, the array nums = [0,1,2,4,5,6,7] might become:
+// [4,5,6,7,0,1,2] if it was rotated 4 times.
+// [0,1,2,4,5,6,7] if it was rotated 7 times.
+// Notice that rotating an array [a[0], a[1], a[2], ..., a[n-1]] 1 time results in the array [a[n-1], a[0], a[1], a[2], ..., a[n-2]].
+// Given the sorted rotated array nums of unique elements, return the minimum element of this array.
+// You must write an algorithm that runs in O(log n) time.
+// Example 1:
+// Input: nums = [3,4,5,1,2]
+// Output: 1
+// Explanation: The original array was [1,2,3,4,5] rotated 3 times.
+// Example 2:
+// Input: nums = [4,5,6,7,0,1,2]
+// Output: 0
+// Explanation: The original array was [0,1,2,4,5,6,7] and it was rotated 4 times.
+// Example 3:
+// Input: nums = [11,13,15,17]
+// Output: 11
+// Explanation: The original array was [11,13,15,17] and it was rotated 4 times. 
+
+public class Solution {
+    public int FindMin(int[] nums) {
+        int left = 0,
+            right = nums.Length-1;
+        while(left < right){
+            if(nums[left] < nums[right])
+                return nums[left];
+            int mid = (right - left)/2 + left;
+            if(nums[mid] < nums[left])
+                right = mid;
+            else
+                left = mid+1;
+        }
+        return nums[left];
+    }
+}

154.FindMin.cs

@@ -0,0 +1,41 @@
+// 154. Find Minimum in Rotated Sorted Array II
+// Suppose an array of length n sorted in ascending order is rotated between 1 and n times. For example, the array nums = [0,1,4,4,5,6,7] might become:
+// [4,5,6,7,0,1,4] if it was rotated 4 times.
+// [0,1,4,4,5,6,7] if it was rotated 7 times.
+// Notice that rotating an array [a[0], a[1], a[2], ..., a[n-1]] 1 time results in the array [a[n-1], a[0], a[1], a[2], ..., a[n-2]].
+// Given the sorted rotated array nums that may contain duplicates, return the minimum element of this array.
+// You must decrease the overall operation steps as much as possible.
+// Example 1:
+// Input: nums = [1,3,5]
+// Output: 1
+// Example 2:
+// Input: nums = [2,2,2,0,1]
+// Output: 0
+
+public class Solution {
+    public int FindMin(int[] nums) {
+        Array.Sort(nums);
+        return nums[0];
+    }
+}
+
+// nums[lo] <= nums[mi] <= nums[hi], min is nums[lo]
+// nums[lo] > nums[mi] <= nums[hi], (lo, mi] is not sorted, min is inside
+// nums[lo] <= nums[mi] > nums[hi], (mi, hi] is not sorted, min is inside
+// nums[lo] > nums[mi] > nums[hi], impossible
+
+public int FindMin(int[] nums) {
+        int left = 0,
+            right = nums.Length-1;
+        while(left < right){
+            int mid = (right - left)/2 + left;
+            if(nums[mid] > nums[right])
+                left = mid + 1;
+            else if (nums[mid] < nums[left])
+                right = mid;
+            else{
+                right--;
+            }
+        }
+        return nums[left];
+    }

17.LetterCombinations.cs

@@ -0,0 +1,34 @@
+// 17. Letter Combinations of a Phone Number
+// Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.
+// A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.
+// Example 1:
+// Input: digits = "23"
+// Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
+// Example 2:
+// Input: digits = ""
+// Output: []
+// Example 3:
+// Input: digits = "2"
+// Output: ["a","b","c"]
+
+public class Solution {
+    string[] dialPad = new string[]
+        {"","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};
+    public IList<string> LetterCombinations(string digits) {
+        IList<string> result = new List<string>();
+        if(digits != ""){
+            AllCombination(result,digits,"", 0);
+        }
+        return result;  
+    }
+    public void AllCombination(IList<string> result,string digits,string s, int idx)    {
+        if(idx == digits.Length){
+            result.Add(new string(s));
+            return;
+        }
+        int num = digits[idx] - '0';
+        foreach(char c in dialPad[num]){
+            AllCombination(result,digits,s + c, idx+1);
+        }
+    }
+}

36.IsValidSudoku.cs

@@ -64,4 +64,35 @@ public bool CheckBox(char[][] board, int row, int col)
         }
         return true;
     }
+}
+
+//HasSet
+public class Solution {
+    public bool IsValidSudoku(char[][] board) {
+        HashSet<int>[] row = new HashSet<int>[9]; 
+        HashSet<int>[] col = new HashSet<int>[9]; 
+        HashSet<int>[] box = new HashSet<int>[9]; 
+        for(int i = 0; i < 9; i++){
+            row[i] = new HashSet<int>();
+            col[i] = new HashSet<int>();
+            box[i] = new HashSet<int>();
+        }
+        for(int i = 0; i < 9; i++){
+            for(int j = 0; j < 9; j++){
+                if(board[i][j] != '.'){
+                    int val = board[i][j] - '0';
+                    if(!row[i].Contains(val) && !col[j].Contains(val) 
+                      && !box[(i/3)*3 + (j/3)].Contains(val)) {
+                        row[i].Add(val);
+                        col[j].Add(val);
+                        box[(i/3)*3 + (j/3)].Add(val);
+                    }
+                    else{
+                        return false;
+                    }
+                }
+            }
+        }
+        return true;
+    }
 }