diff --git a/arrays/src/arrays/Main.java b/arrays/src/arrays/Main.java
index 84c6c76..0925372 100644
--- a/arrays/src/arrays/Main.java
+++ b/arrays/src/arrays/Main.java
@@ -37,7 +37,67 @@ class Sieve implements Iterator<Integer> {
     }
 }
 
+class Sudoku {
+    static boolean solved(int[][] puz) {
+        // First check the data is shaped correctly.
+        if (puz.length != 9) return false;
+        for (int[] row : puz)
+            if (row.length != 9) return false;
+
+        // Make sure they're all valid integers.
+        for (int[] row : puz)
+            for (int n : row)
+                if (n < 1 || n > 9) return false;
+
+        // Check that there'ren't any repeats in a row.
+        for (int[] row : puz) { int[] }
+    }
+}
+
 class Examples {
+    void testSudoku(Tester t) {
+        int[][] testPuz1 = {
+            {5, 3, 4, 6, 7, 8, 9, 1, 2}, {6, 7, 2, 1, 9, 5, 3, 4, 8},
+            {1, 9, 8, 3, 4, 2, 5, 6, 7}, {8, 5, 9, 7, 6, 1, 4, 2, 3},
+            {4, 2, 6, 8, 5, 3, 7, 9, 1}, {7, 1, 3, 9, 2, 4, 8, 5, 6},
+            {9, 6, 1, 5, 3, 7, 2, 8, 4}, {2, 8, 7, 4, 1, 9, 6, 3, 5},
+            {3, 4, 5, 2, 8, 6, 1, 7, 9}
+        };
+        int[][] testPuz2 = {
+            {5, 3, 4, 6, 7, 8, 9, 1, 2}, {6, 7, 2, 1, 9, 5, 3, 4, 8},
+            {1, 9, 8, 3, 4, 2, 5, 6, 7}, {8, 5, 9, 7, 6, 1, 4, 2, 3},
+            {4, 2, 6, 8, 5, 3, 7, 9, 1}, {7, 1, 3, 9, 2, 4, 8, 5, 6},
+            {9, 6, 4, 5, 3, 7, 2, 8, 4}, // There're 2 4s here.
+            {2, 8, 7, 4, 1, 9, 6, 3, 5}, {3, 4, 5, 2, 8, 6, 1, 7, 9}
+        };
+        int[][] testPuz3 = {
+            // Incomplete, missing a row.
+            {5, 3, 4, 6, 7, 8, 9, 1, 2}, {6, 7, 2, 1, 9, 5, 3, 4, 8},
+            {1, 9, 8, 3, 4, 2, 5, 6, 7}, {8, 5, 9, 7, 6, 1, 4, 2, 3},
+            {4, 2, 6, 8, 5, 3, 7, 9, 1}, {7, 1, 3, 9, 2, 4, 8, 5, 6},
+            {2, 8, 7, 4, 1, 9, 6, 3, 5}, {3, 4, 5, 2, 8, 6, 1, 7, 9}
+        };
+        int[][] testPuz4 = {
+            {5, 3, 4, 6, 7, 8, 9, 1, 2}, {6, 7, 2, 1, 9, 5, 3, 4, 8},
+            {1, 9, 8, 3, 4, 2, 5, 6, 7}, {8, 5, 9, 7, 6, 1, 4, 2, 3},
+            {4, 2, 6, 8, 5, 3, 7, 9, 1}, {7, 1, 3, 9, 2, 4, 8, 5, 6},
+            {9, 6, 1, 5, 3, 7, 2, 8, 4}, {2, 8, 7, 4, 1, 9, 6, 3, 5},
+            {3, 4, 5, 8, 6, 1, 7, 9} // Incomplete, missing a number.
+        };
+        int[][] testPuz5 = {
+            {5, 3, 4, 6, 7, 8, 9, 1, 2}, {6, 7, 2, 1, 9, 5, 3, 4, 8},
+            {1, 9, 8, 3, 4, 2, 5, 6, 7}, {8, 5, 9, 7, 6, 1, 4, 2, 3},
+            {4, 2, 6, 0, 5, 3, 7, 9, 1}, // Invalid number.
+            {7, 1, 3, 9, 2, 4, 8, 5, 6}, {9, 6, 1, 5, 3, 7, 2, 8, 4},
+            {2, 8, 7, 4, 1, 9, 6, 3, 5}, {3, 4, 5, 2, 8, 6, 1, 7, 9}
+        };
+
+        t.checkExpect(Sudoku.solved(testPuz1), true);
+        t.checkExpect(Sudoku.solved(testPuz2), false);
+        t.checkExpect(Sudoku.solved(testPuz3), false);
+        t.checkExpect(Sudoku.solved(testPuz4), false);
+        t.checkExpect(Sudoku.solved(testPuz5), false);
+    }
     void testSieve(Tester t) {
         Sieve sieve = new Sieve(29);
         t.checkExpect(sieve.hasNext(), true);