Create 1079. Letter Tile Possibilities

1079. Letter Tile Possibilities

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+class Solution {
+public:
+    void count(vector<int> &arr, int n, int &ans){
+        //checks if every place is filled.
+        if(n <= 0) return; 
+        //checking for letters which can be filled at nth index.
+        for(int i = 0; i < 26; i++){
+            if(arr[i] > 0){
+                // Reducing its occurence.
+                arr[i]--; 
+                ans++;
+                count(arr, n - 1, ans);
+                //Restoring its occurence for furthur combination./Backtracking.
+                arr[i]++;
+            }
+        }
+    }
+    int numTilePossibilities(string tiles) {
+        vector<int> arr(26, 0);
+        //Occurence count array.
+        for(int i = 0; i < tiles.size(); i++){
+            arr[int(tiles[i]) - 65]++;
+        }
+        int ans = 0; 
+        count(arr, tiles.size(), ans); 
+        return ans; 
+    }
+};