diff --git a/src/advanced.cpp b/src/advanced.cpp
index 698c286..aca9f0e 100644
--- a/src/advanced.cpp
+++ b/src/advanced.cpp
@@ -27,11 +27,13 @@ void Execute(int row, int column) {
   PrintMap();
   std::cout.rdbuf(old_output_buffer);  // Restore the output buffer
   str = oss.str();                     // Read the output
+  // debug: output status of map to original stdout
+  PrintMap();
   std::istringstream iss(str);  // Redirect the input to the string, which
                                 // stores the output recently
   std::streambuf *old_input_buffer = std::cin.rdbuf();
   ReadMap();
-  std::cin.rdbuf(old_input_buffer);
+  std::cin.rdbuf(old_input_buffer);  // Restore the input buffer
 }
 
 int main() {
diff --git a/src/include/client.h b/src/include/client.h
index 6126ad7..5fe14f1 100644
--- a/src/include/client.h
+++ b/src/include/client.h
@@ -4,6 +4,8 @@
 #include <cassert>
 #include <cstring>
 #include <iostream>
+#include <queue>
+#include <random>
 #include <utility>
 
 extern int rows;     // The count of rows of the game map
@@ -49,15 +51,71 @@ void InitGame() {
  *     01?
  */
 namespace Client {
+const unsigned int RndSeed = std::random_device{}();
+std::mt19937 RawRnd(RndSeed);  // a basic random generator
 const int max_size = 35;
-char game_map[max_size][max_size];
+char game_map[max_size][max_size];  // store the raw game map in format of char
+std::queue<std::pair<int, int> >
+    no_mine_block_to_be_clicked;  // store the block that definitely has no mine
+                                  // and not yet clicked
+int map_status[max_size]
+              [max_size];  // store the status of each block(processed version),
+                           // 0 means unknown , -1 means has mine, 1 means no
+                           // mine and not yet clicked, and 2 means has been
+                           // clicked Note that if some block is found to be
+                           // definitely has no mine or has mine, it will be
+                           // marked as known even if it is not clicked. In
+                           // conclusion, if map_status[i][j] == 0, then
+                           // game_map[i][j] == '?'. If map_status[i][j] == -1,
+                           // then game_map[i][j] == '?', and it will never be
+                           // clicked. If map_status[i][j] == 1, then
+                           // game_map[i][j] == '?', and it will be clicked
+                           // later. If map_status[i][j] == 2, then
+                           // game_map[i][j] == '0'-'8', and it has been clicked
+                           // And when a block's status is updated from 0 to 1,
+                           // it will be pushed into no_mine_block_to_be_clicked
 /**
  * @brief The definition of function PreProcessData()
  *
  * @details This function is designed to preprocess the data of the game map
  * immedietly after reading it.
+ * It will check unknown blocks and use Gaussian Elimination to find if there is
+ * any block that definitely has no mine or has mine. If there is a block
+ * definitely has no mine, it will push the block into
+ * no_mine_block_to_be_clicked.
+ * Note that if some block is found to be definitely has no mine or has mine, it
+ * will be marked as known even if it is not clicked.
  */
-void PreProcessData() { using namespace Client; }
+void PreProcessData() {
+  using namespace Client;
+  // scan the game_map and mark clicked block in map_status
+  for (int i = 0; i < rows; i++)
+    for (int j = 0; j < columns; j++)
+      if (game_map[i][j] != '?') {
+        assert(game_map[i][j] >= '0' && game_map[i][j] <= '8');
+        map_status[i][j] = 2;
+        // special process for 0 before Gaussian Elimination starts
+        if (game_map[i][j] == '0') {
+          for (int k = i - 1; k <= i + 1; k++)
+            for (int l = j - 1; l <= j + 1; l++)
+              if (k >= 0 && k < rows && l >= 0 && l < columns &&
+                  map_status[k][l] == 0) {
+                map_status[k][l] = 1;
+                no_mine_block_to_be_clicked.push(std::make_pair(k, l));
+              }
+        }
+      }
+}
+/**
+ * @brief The definition of function MakeBestGuess()
+ *
+ * @details This function is designed to make the best guess when there is no
+ * definite none-mine block to be clicked.
+ */
+std::pair<int, int> MakeBestGuess() {
+  using namespace Client;
+  return std::make_pair(0, 0);
+}
 /**
  * @brief The definition of function GenerateNextStep()
  *
@@ -66,7 +124,12 @@ void PreProcessData() { using namespace Client; }
  */
 std::pair<int, int> GenerateNextStep() {
   using namespace Client;
-  return std::make_pair(0, 0);
+  if (!no_mine_block_to_be_clicked.empty()) {
+    std::pair<int, int> next_step = no_mine_block_to_be_clicked.front();
+    no_mine_block_to_be_clicked.pop();
+    return next_step;
+  } else
+    return MakeBestGuess();
 }
 }  // namespace Client
 void ReadMap() {