Create sum-of-subsequence-widths.cpp

Author: kamyu104

C++/sum-of-subsequence-widths.cpp

@@ -0,0 +1,18 @@
+// Time:  O(n)
+// Spce:  O(1)
+
+class Solution {
+public:
+    int sumSubseqWidths(vector<int>& A) {
+        static const int M = 1e9 + 7;
+        sort(A.begin(), A.end());
+        // sum(A[i] * (2^i - 2^(len(A)-1-i))), i = 0..len(A)-1
+        // <=>
+        // sum(((A[i] - A[len(A)-1-i]) * 2^i), i = 0..len(A)-1
+        int64_t result = 0l, c = 1l;
+        for (int i = 0; i < A.size(); ++i, c = (c << 1) % M) {
+            result = (result + (A[i] - A[A.size() - 1 - i]) * c % M) % M;
+        }
+        return (result + M) % M;
+    }
+};