add 957

Author: fishercoder1534

README.md

@@ -234,6 +234,7 @@ _If you like this project, please leave me a star._ ★
 |965|[Univalued Binary Tree](https://leetcode.com/problems/univalued-binary-tree/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_965.java) | |Easy| DFS, recursion|
 |961|[N-Repeated Element in Size 2N Array](https://leetcode.com/problems/n-repeated-element-in-size-2n-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_961.java) | |Easy|
 |958|[Check Completeness of a Binary Tree](https://leetcode.com/problems/check-completeness-of-a-binary-tree/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_958.java) | |Medium|Tree
+|957|[Prison Cells After N Days](https://leetcode.com/problems/prison-cells-after-n-days/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_957.java) | |Medium|
 |954|[Array of Doubled Pairs](https://leetcode.com/problems/array-of-doubled-pairs/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_954.java) |  [:tv:](https://youtu.be/Q0WKzdpR74o)|Medium|
 |953|[Verifying an Alien Dictionary](https://leetcode.com/problems/verifying-an-alien-dictionary/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_953.java)| |Easy|
 |951|[Flip Equivalent Binary Trees](https://leetcode.com/problems/flip-equivalent-binary-trees/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_951.java) | |Medium| Tree, DFS, recursion|

src/main/java/com/fishercoder/solutions/_957.java

@@ -0,0 +1,46 @@
+package com.fishercoder.solutions;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+
+public class _957 {
+    public static class Solution1 {
+        public int[] prisonAfterNDays(int[] cells, int N) {
+            Set<String> prisonStates = new HashSet<>();
+            boolean hasCycle = false;
+            int times = 0;
+            for (int i = 0; i < N; i++) {
+                int[] next = getNextDay(cells);
+                String nextDayState = Arrays.toString(next);
+                if (prisonStates.contains(nextDayState)) {
+                    hasCycle = true;
+                    break;
+                } else {
+                    prisonStates.add(nextDayState);
+                    times++;
+                }
+                cells = next;
+            }
+            if (hasCycle) {
+                N %= times;
+                for (int i = 0; i < N; i++) {
+                    cells = getNextDay(cells);
+                }
+            }
+            return cells;
+        }
+
+        private int[] getNextDay(int[] cells) {
+            int[] nextDay = new int[cells.length];
+            for (int i = 0; i < cells.length; i++) {
+                if (i == 0 || i == cells.length - 1) {
+                    nextDay[i] = 0;
+                } else {
+                    nextDay[i] = (cells[i - 1] == cells[i + 1]) ? 1 : 0;
+                }
+            }
+            return nextDay;
+        }
+    }
+}

src/test/java/com/fishercoder/_957Test.java

@@ -0,0 +1,36 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._957;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertArrayEquals;
+
+public class _957Test {
+    private static _957.Solution1 solution1;
+    private static int[] cells;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _957.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        cells = new int[]{0, 1, 0, 1, 1, 0, 0, 1};
+        assertArrayEquals(new int[]{0, 0, 1, 1, 0, 0, 0, 0}, solution1.prisonAfterNDays(cells, 7));
+    }
+
+    @Test
+    public void test2() {
+        cells = new int[]{1, 0, 0, 1, 0, 0, 1, 0};
+        assertArrayEquals(new int[]{0, 0, 1, 1, 1, 1, 1, 0}, solution1.prisonAfterNDays(cells, 1000000000));
+    }
+
+    @Test
+    public void test3() {
+        cells = new int[]{0, 1, 1, 1, 0, 0, 0, 0};
+        assertArrayEquals(new int[]{0, 0, 1, 0, 0, 1, 1, 0}, solution1.prisonAfterNDays(cells, 99));
+    }
+
+}