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Author: assassint2017

Word Search/Word_Search.cpp

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+// 典型的回溯
+// Runtime: 28 ms, faster than 75.07% of C++ online submissions for Word Search.
+// Memory Usage: 12.5 MB, less than 52.94% of C++ online submissions for Word Search.
+
+class Solution
+{
+public:
+	bool exist(vector<vector<char>>& matrix, string word)
+	{
+		// 边界条件处理
+		if (word.size() == 0) return false;
+
+		int row = matrix.size();
+		if (row == 0) return false;
+
+		int col = matrix[0].size();
+		if (col == 0) return false;
+
+		// 循环查找
+		vector<vector<bool>> visited(row, vector<bool>(col, false));
+		for (int i = 0; i < row; ++i)
+		{
+			for (int j = 0; j < col; ++j)
+			{
+				if (matrix[i][j] == word[0])
+				{
+					visited[i][j] = true;
+
+					if (dfs(matrix, word, visited, i, j, 1))
+						return true;
+
+					visited[i][j] = false;
+				}
+			}
+		}
+		return false;
+	}
+private:
+	bool dfs(const vector<vector<char>>& matrix, const string& word, vector<vector<bool>>& visited, int starti, int startj, int start)
+	{
+		if (start == word.length())
+			return true;
+		else
+		{
+			// 向上寻找
+			if (starti - 1 >= 0 && !visited[starti - 1][startj] && matrix[starti - 1][startj] == word[start])
+			{
+				visited[starti - 1][startj] = true;
+				if (dfs(matrix, word, visited, starti - 1, startj, start + 1))
+					return true;
+				visited[starti - 1][startj] = false;
+			}
+
+			// 向下寻找
+			if (starti + 1 < matrix.size() && !visited[starti + 1][startj] && matrix[starti + 1][startj] == word[start])
+			{
+				visited[starti + 1][startj] = true;
+				if (dfs(matrix, word, visited, starti + 1, startj, start + 1))
+					return true;
+				visited[starti + 1][startj] = false;
+			}
+
+			// 向左寻找
+			if (startj - 1 >= 0 && !visited[starti][startj - 1] && matrix[starti][startj - 1] == word[start])
+			{
+				visited[starti][startj - 1] = true;
+				if (dfs(matrix, word, visited, starti, startj - 1, start + 1))
+					return true;
+				visited[starti][startj - 1] = false;
+			}
+
+			// 向右寻找
+			if (startj + 1 < matrix[0].size() && !visited[starti][startj + 1] && matrix[starti][startj + 1] == word[start])
+			{
+				visited[starti][startj + 1] = true;
+				if (dfs(matrix, word, visited, starti, startj + 1, start + 1))
+					return true;
+				visited[starti][startj + 1] = false;
+			}
+
+			return false;
+		}
+	}
+};