Create longest-ideal-subsequence.cpp

Author: kamyu104

C++/longest-ideal-subsequence.cpp

@@ -0,0 +1,15 @@
+// Time:  O(n)
+// Space: O(1)
+
+// dp
+class Solution {
+public:
+    int longestIdealString(string s, int k) {
+        vector<int> dp(26);
+        for (const auto& c : s) {
+            const int x = c - 'a';
+            dp[x] = *max_element(cbegin(dp) + max(x - k, 0), cbegin(dp) + min(x + k + 1, 26)) + 1;
+        }
+        return *max_element(cbegin(dp), cend(dp));
+    }
+};