Add solutions for leetcode 73.

yanglr · yanglr · commit 8335b2b75fe7 · 2021-09-13T08:14:43.000+08:00
diff --git a/cpp-leetcode/leetcode73-word-search_dfs1_naive.cpp b/cpp-leetcode/leetcode73-word-search_dfs1_naive.cpp
@@ -0,0 +1,60 @@
+#include <vector>
+#include <iostream>
+using namespace std;
+
+class Solution {
+public:
+    bool exist(vector<vector<char>>& board, string word) {
+        int m = board.size();
+        int n = board[0].size();
+        vector<vector<int>> visited(m, vector<int>(n, 0));
+        for (int i = 0; i < m; i++)
+        {
+            for (int j = 0; j < n; j++)
+            {
+                if (dfs(board, i, j, visited, word, 0))
+                    return true;
+            }                
+        }
+        return false;
+    }
+    // 是否能找到index = curPos处的字符, curPos: 在目标单词中的index
+    bool dfs(vector<vector<char>>& board, int x, int y, vector<vector<int>>& visited, string word, int curPos)
+    {
+        if (curPos == word.size()) return true;
+        int m = board.size();
+        int n = board[0].size();        
+        if (x < 0 || x >= m || y < 0 || y >= n) return false;
+        if (visited[x][y] == 1) return false;
+        if (board[x][y] != word[curPos]) return false;
+        vector<pair<int, int>> dirs({{1, 0}, {-1, 0}, {0, 1}, {0, -1}}); // 右/左/上/下
+        visited[x][y] = 1;
+        for (auto dir : dirs)
+        {
+            auto dirX = dir.first;
+            auto dirY = dir.second;
+            if (dfs(board, x + dirX, y + dirY, visited, word, curPos + 1)) return true;
+        }
+        visited[x][y] = 0;
+
+        return false;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    vector<vector<char>> board 
+    {
+        {'A', 'B', 'C', 'E'}, 
+        {'S', 'F', 'C', 'S'}, 
+        {'A', 'D', 'E', 'E'}
+    };
+    string word = "ABCCED";
+
+    bool isValid = sol.exist(board, word);
+    cout << (isValid == true ? "true" : "false") << endl;
+
+    return 0;
+}
diff --git a/cpp-leetcode/leetcode73-word-search_dfs1_optimize_direction_vectors.cpp b/cpp-leetcode/leetcode73-word-search_dfs1_optimize_direction_vectors.cpp
@@ -0,0 +1,59 @@
+#include <vector>
+#include <iostream>
+using namespace std;
+
+class Solution {
+public:
+    bool exist(vector<vector<char>>& board, string word) {
+        int m = board.size();
+        int n = board[0].size();
+        vector<vector<int>> visited(m, vector<int>(n, 0));
+        for (int i = 0; i < m; i++)
+        {
+            for (int j = 0; j < n; j++)
+            {
+                if (dfs(board, i, j, visited, word, 0))
+                    return true;
+            }                
+        }
+        return false;
+    }
+    // 是否能找到index = curPos处的字符, curPos: 在目标单词中的index
+    bool dfs(vector<vector<char>>& board, int x, int y, vector<vector<int>>& visited, string& word, int curPos)
+    {
+        if (curPos == word.size()) return true;
+        int m = board.size();
+        int n = board[0].size();        
+        if (x < 0 || x >= m || y < 0 || y >= n) return false;
+        if (visited[x][y] == 1) return false;
+        if (board[x][y] != word[curPos]) return false;
+
+        int dx[4] = {-1, 1, 0, 0}, dy[4] = {0, 0, 1, -1}; /* 方向变量不使用vector<pair>, 速度会变快, 依次表示右/左/上/下 */
+        visited[x][y] = 1;
+        for (int i = 0; i < 4; i++)
+        {
+            if (dfs(board, x + dx[i], y + dy[i], visited, word, curPos + 1)) return true;
+        }
+        visited[x][y] = 0;
+
+        return false;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    vector<vector<char>> board 
+    {
+        {'A', 'B', 'C', 'E'}, 
+        {'S', 'F', 'C', 'S'}, 
+        {'A', 'D', 'E', 'E'}
+    };
+    string word = "ABCCED";
+
+    bool isValid = sol.exist(board, word);
+    cout << (isValid == true ? "true" : "false") << endl;
+
+    return 0;
+}
diff --git a/cpp-leetcode/leetcode73-word-search_dfs1_using_global_vars.cpp b/cpp-leetcode/leetcode73-word-search_dfs1_using_global_vars.cpp
@@ -0,0 +1,63 @@
+#include <vector>
+#include <iostream>
+using namespace std;
+
+class Solution {
+    vector<vector<char>> M;
+    string str;
+public:
+    bool exist(vector<vector<char>>& board, string word) {
+        M = board;
+        str = word;
+        int m = M.size();
+        int n = M[0].size();
+        vector<vector<int>> visited(m, vector<int>(n, 0));
+        for (int i = 0; i < m; i++)
+        {
+            for (int j = 0; j < n; j++)
+            {
+                if (dfs(i, j, visited, 0))
+                    return true;
+            }                
+        }
+        return false;
+    }
+    bool dfs(int x, int y, vector<vector<int>>& visited, int curPos)
+    {
+        if (curPos == str.size()) return true;
+        int m = M.size();
+        int n = M[0].size();        
+        if (x < 0 || x >= m || y < 0 || y >= n) return false;
+        if (visited[x][y] == 1) return false;
+        if (M[x][y] != str[curPos]) return false;
+        vector<pair<int, int>> dirs = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}}; // 右/左/上/下
+        visited[x][y] = 1;
+        for (auto dir : dirs)
+        {
+            auto dirX = dir.first;
+            auto dirY = dir.second;
+            if (dfs(x + dirX, y + dirY, visited, curPos + 1)) return true;
+        }
+        visited[x][y] = 0;
+
+        return false;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    vector<vector<char>> board 
+    {
+        {'A', 'B', 'C', 'E'}, 
+        {'S', 'F', 'C', 'S'}, 
+        {'A', 'D', 'E', 'E'}
+    };
+    string word = "ABCCED";
+
+    bool isValid = sol.exist(board, word);
+    cout << (isValid == true ? "true" : "false") << endl;
+
+    return 0;
+}
diff --git a/cpp-leetcode/leetcode73-word-search_dfs3_no_visited_array.cpp b/cpp-leetcode/leetcode73-word-search_dfs3_no_visited_array.cpp
@@ -0,0 +1,59 @@
+#include <vector>
+#include <iostream>
+using namespace std;
+
+class Solution {
+public:
+    bool exist(vector<vector<char>>& board, string word) {
+        int m = board.size();
+        int n = board[0].size();
+        for (int i = 0; i < m; i++)
+        {
+            for (int j = 0; j < n; j++)
+            {
+                if (dfs(board, i, j, word, 0))
+                    return true;
+            }                
+        }
+        return false;
+    }
+
+    bool dfs(vector<vector<char>>& board, int x, int y, string& str, int curPos)
+    {
+        if (board[x][y] != str[curPos]) return false;
+        if (curPos == str.size() - 1) return true;
+        int dx[4] = {-1, 1, 0, 0}, dy[4] = {0, 0, 1, -1}; /* 推荐写法: 使用两个定长数组做方向向量, 右/左/上/下 */
+        char ch = board[x][y];
+        board[x][y] = '*';     /* word中只含有英文字母, 这里用英文字母以外的字符都行, 比如使用星号  */
+        for (int i = 0; i < 4; i++)
+        {
+            int newX = x + dx[i], newY = y + dy[i];
+            if (newX >= 0 && newX < board.size() && newY >= 0 && newY < board[0].size())
+            {
+                if (dfs(board, newX, newY, str, curPos + 1))
+                    return true;
+            }
+        }
+        board[x][y] = ch;
+
+        return false;
+    }
+};
+
+// Test
+int main()
+{
+    Solution sol;
+    vector<vector<char>> board 
+    {
+        {'A', 'B', 'C', 'E'}, 
+        {'S', 'F', 'C', 'S'}, 
+        {'A', 'D', 'E', 'E'}
+    };
+    string word = "ABCCED";
+
+    bool isValid = sol.exist(board, word);
+    cout << (isValid == true ? "true" : "false") << endl;
+
+    return 0;
+}
