cpp: add «1143. Longest Common Subsequence»

Signed-off-by: Matej Focko <me@mfocko.xyz>

cpp/longest-common-subsequence.cpp

@@ -0,0 +1,45 @@
+#include <cassert>
+#include <string>
+#include <vector>
+
+class Solution {
+    auto dp_helper(const std::string &t1, const std::string &t2,
+                   std::vector<int> &dp, int i, int j) -> int {
+        if (i < 0 || j < 0) {
+            return 0;
+        }
+
+        auto idx = i * t2.size() + j;
+        if (dp[idx] != -1) {
+            return dp[idx];
+        }
+
+        if (t1[i] == t2[j]) {
+            dp[idx] = 1 + dp_helper(t1, t2, dp, i - 1, j - 1);
+        } else {
+            dp[idx] = std::max(dp_helper(t1, t2, dp, i - 1, j),
+                               dp_helper(t1, t2, dp, i, j - 1));
+        }
+
+        return dp[idx];
+    }
+
+  public:
+    auto longestCommonSubsequence(const std::string &text1,
+                                  const std::string &text2) -> int {
+        int m = text1.size();
+        int n = text2.size();
+        std::vector<int> dp(m * n, -1);
+        return dp_helper(text1, text2, dp, m - 1, n - 1);
+    }
+};
+
+int main() {
+    Solution s;
+
+    assert(s.longestCommonSubsequence("abcde", "ace") == 3);
+    assert(s.longestCommonSubsequence("abc", "abc") == 3);
+    assert(s.longestCommonSubsequence("abc", "def") == 0);
+
+    return 0;
+}