cpp: add «752. Open the Lock»

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

cpp/open-the-lock.cpp

@@ -0,0 +1,53 @@
+#include <queue>
+#include <string>
+#include <vector>
+
+class Solution {
+  public:
+    int openLock(const std::vector<std::string> &deadends,
+                 const std::string &target) {
+        std::vector<bool> visited(10000);
+        for (const auto &end : deadends) {
+            visited[std::stoi(end)] = true;
+        }
+
+        // we're already starting with a dead end
+        if (visited[0]) {
+            return -1;
+        }
+
+        auto t = std::stoi(target);
+
+        std::queue<std::pair<int, int>> q;
+        q.emplace(0, 0);
+        visited[0] = true;
+
+        while (!q.empty()) {
+            auto [steps, comb] = q.front();
+            q.pop();
+
+            // found the target
+            if (comb == t) {
+                return steps;
+            }
+
+            auto comb_tmp = comb;
+            for (auto d = 1; d < 10000; d *= 10) {
+                auto digit = comb_tmp % 10;
+                comb_tmp /= 10;
+
+                for (auto i : {-1, 1}) {
+                    auto next_digit = (digit + i + 10) % 10;
+                    auto next_comb = comb + (next_digit - digit) * d;
+
+                    if (!visited[next_comb]) {
+                        q.emplace(steps + 1, next_comb);
+                        visited[next_comb] = true;
+                    }
+                }
+            }
+        }
+
+        return -1;
+    }
+};