[feat ]: leetcode 752

Signed-off-by: Bo-Wei Chen(BWbwchen) <tim.chenbw@gmail.com>

Author: BWbwchen

leetcode/0752_Open-the-Lock.cpp

@@ -0,0 +1,56 @@
+class Solution {
+public:
+    struct si {
+        string s;
+        int steps;
+    };
+    string rotate(string s, int i, int dir) {
+        s[i] = (((s[i] - '0') + dir + 10) % 10) + '0';
+        return s;
+    }
+    int openLock(vector<string>& deadends, string target) {
+        // bfs with graph, which consist of 10000 nodes.
+        // each node has 8 neighbors.
+        queue<si> q;
+        vector<int> dirs = {-1, 1};
+
+        unordered_set<string> dead;
+        for (auto &s : deadends) {
+            dead.insert(s);
+        }
+
+        if (dead.count("0000") <= 0)
+            q.push(si(
+                "0000",
+                0
+            ));
+
+        unordered_set<string> found;
+        found.insert("0000");
+
+        bool is_valid = false;
+        int ret = std::numeric_limits<int>::max();
+
+        while (!q.empty()) {
+            auto top = q.front();
+            q.pop();
+
+            if (top.s == target) {
+                return top.steps;
+            }
+
+            for (int i = 0; i < 4; ++i) {
+                for (auto dir : dirs) {
+                    auto new_str = rotate(top.s, i, dir);
+                    if (dead.count(new_str) <= 0 && found.count(new_str) <= 0) {
+                        q.push(si(new_str, top.steps+1));
+                        found.insert(new_str);
+                    }
+                }
+            }
+        }
+
+
+        return -1;
+    }
+};