Solve LeetCode #79 'Word Search' [Medium].

LeetCode/src/LeetCode.Challenges/Problems00xx/N_0079_WordSearch/Solution.cs

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+namespace LeetCode.Challenges.Problems00xx.N_0079_WordSearch;
+
+public static class Solution
+{
+    public static bool Exist(char[][] board, string word)
+    {
+        var rows = board.Length;
+        var cols = board[0].Length;
+        var visited = new bool[rows, cols];
+
+        for (int row = 0; row < rows; row++)
+        {
+            for (int col = 0; col < cols; col++)
+            {
+                if (Dfs(row, col, 0))
+                {
+                    return true;
+                }
+            }
+        }
+
+        return false;
+
+        bool Dfs(int i, int j, int index)
+        {
+            if (i < 0 || i >= rows || j < 0 || j >= cols || visited[i, j] || board[i][j] != word[index])
+            {
+                return false;
+            }
+
+            if (index == word.Length - 1)
+            {
+                return true;
+            }
+
+            visited[i, j] = true;
+
+            bool found =
+                Dfs(i + 1, j, index + 1) ||
+                Dfs(i - 1, j, index + 1) ||
+                Dfs(i, j + 1, index + 1) ||
+                Dfs(i, j - 1, index + 1);
+
+            visited[i, j] = false;
+
+            return found;
+        }
+    }
+}

LeetCode/tests/LeetCode.Challenges.UnitTests/Problems00xx/N_0079_WordSearch/SolutionTests.cs

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+using LeetCode.Challenges.Problems00xx.N_0079_WordSearch;
+using Shouldly;
+using Xunit;
+
+namespace LeetCode.Challenges.UnitTests.Problems00xx.N_0079_WordSearch;
+
+public class SolutionTests
+{
+    [Theory]
+    [MemberData(nameof(TestData))]
+    public void GivenNumbers_WhenSubsets_ThenResultAsExpected(char[][] board, string word, bool expectedResult)
+    {
+        Solution.Exist(board, word).ShouldBe(expectedResult);
+    }
+
+    public static IEnumerable<object[]> TestData()
+    {
+        yield return
+        [
+            new char[][]
+            {
+                ['A', 'B', 'C', 'E'],
+                ['S', 'F', 'C', 'S'],
+                ['A', 'D', 'E', 'E']
+            },
+            "ABCCED",
+            true
+        ];
+
+        yield return
+        [
+            new char[][]
+            {
+                ['A', 'B', 'C', 'E'],
+                ['S', 'F', 'C', 'S'],
+                ['A', 'D', 'E', 'E']
+            },
+            "SEE",
+            true
+        ];
+
+        yield return
+        [
+            new char[][]
+            {
+                [ 'A', 'B', 'C', 'E' ],
+                [ 'S', 'F', 'C', 'S' ],
+                [ 'A', 'D', 'E', 'E' ]
+            },
+            "ABCB",
+            false
+        ];
+    }
+}