Create number-of-ways-to-select-buildings.cpp

Author: kamyu104

C++/number-of-ways-to-select-buildings.cpp

@@ -0,0 +1,19 @@
+// Time:  O(k * n) = O(n)
+// Space: O(k) = O(1)
+
+// dp
+class Solution {
+public:
+    long long numberOfWays(string s) {
+        static const int K = 3;
+        vector<vector<int64_t>> dp(K, vector<int64_t>(2));  // dp[i][j]: number of ways of selecting i+1 buildings ending with type j
+        for (const auto& c : s) {
+            int j = c - '0';
+            ++dp[0][j];
+            for (int i = 1; i < size(dp); ++i) {
+                dp[i][j] += dp[i - 1][1 ^ j];
+            }
+        }
+        return dp.back()[0] + dp.back()[1];
+    }
+};