Create 1915. Number of Wonderful Substrings (#469)

Author: Chayandas07

1915. Number of Wonderful Substrings

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+class Solution {
+public:
+    long long wonderfulSubstrings(string word) {
+        unordered_map<int, int> count;
+        int mask = 0;
+        count[0] = 1;
+        long long result = 0;
+        for(char c : word) {
+            mask ^= 1 << (c - 'a');
+            result += count[mask];
+            for(int i = 0; i < 10; i++) {
+                result += count[mask ^ (1 << i)];
+            }
+            count[mask]++;
+        }
+        return result;
+    }
+};