add 1349

fishercoder1534 · fishercoder1534 · commit a5619c83a6ff · 2020-02-09T17:28:27.000-08:00
diff --git a/README.md b/README.md
@@ -8,6 +8,7 @@ _If you like this project, please leave me a star._ &#9733;
 
 |  #  |      Title     |   Solutions   | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|--------|-------------|-------------
+|1349|[Maximum Students Taking Exam](https://leetcode.com/problems/maximum-students-taking-exam/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1349.java) | |Hard|Dynamic Programming|
 |1348|[Tweet Counts Per Frequency](https://leetcode.com/problems/tweet-counts-per-frequency/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1348.java) | |Medium|Design|
 |1347|[Minimum Number of Steps to Make Two Strings Anagram](https://leetcode.com/problems/minimum-number-of-steps-to-make-two-strings-anagram/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1347.java) | |Easy|String|
 |1346|[Check If N and Its Double Exist](https://leetcode.com/problems/check-if-n-and-its-double-exist/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1346.java) | |Easy|Array|
diff --git a/src/main/java/com/fishercoder/solutions/_1349.java b/src/main/java/com/fishercoder/solutions/_1349.java
@@ -0,0 +1,82 @@
+package com.fishercoder.solutions;
+
+import java.util.Arrays;
+
+/**
+ * 1349. Maximum Students Taking Exam
+ *
+ * Given a m * n matrix seats  that represent seats distributions in a classroom.
+ * If a seat is broken, it is denoted by '#' character otherwise it is denoted by a '.' character.
+ * Students can see the answers of those sitting next to the left, right, upper left and upper right, but he cannot see the answers of the student sitting directly in front or behind him. Return the maximum number of students that can take the exam together without any cheating being possible..
+ * Students must be placed in seats in good condition.
+ *
+ * Example 1:
+ * Input: seats = [["#",".","#","#",".","#"],
+ *                 [".","#","#","#","#","."],
+ *                 ["#",".","#","#",".","#"]]
+ * Output: 4
+ * Explanation: Teacher can place 4 students in available seats so they don't cheat on the exam.
+ *
+ * Example 2:
+ * Input: seats = [[".","#"],
+ *                 ["#","#"],
+ *                 ["#","."],
+ *                 ["#","#"],
+ *                 [".","#"]]
+ * Output: 3
+ * Explanation: Place all students in available seats.
+ *
+ * Example 3:
+ * Input: seats = [["#",".",".",".","#"],
+ *                 [".","#",".","#","."],
+ *                 [".",".","#",".","."],
+ *                 [".","#",".","#","."],
+ *                 ["#",".",".",".","#"]]
+ * Output: 10
+ * Explanation: Place students in available seats in column 1, 3 and 5.
+ *
+ * Constraints:
+ * seats contains only characters '.' and'#'.
+ * m == seats.length
+ * n == seats[i].length
+ * 1 <= m <= 8
+ * 1 <= n <= 8
+ * */
+public class _1349 {
+    public static class Solution1 {
+        /**credit: https://leetcode.com/problems/maximum-students-taking-exam/discuss/503686/A-simple-tutorial-on-this-bitmasking-problem*/
+        public int maxStudents(char[][] seats) {
+            int m = seats.length;
+            int n = seats[0].length;
+            int[] validRows = new int[m];
+            for (int i = 0; i < m; i++) {
+                for (int j = 0; j < n; j++) {
+                    validRows[i] = (validRows[i] << 1) + (seats[i][j] == '.' ? 1 : 0);
+                }
+            }
+            int stateSize = 1 << n; // There are 2^n states for n columns in binary format
+            int[][] dp = new int[m][stateSize];
+            for (int i = 0; i < m; i++) {
+                Arrays.fill(dp[i], -1);
+            }
+            int ans = 0;
+            for (int i = 0; i < m; i++) {
+                for (int j = 0; j < stateSize; j++) {
+                    if (((j & validRows[i]) == j) && ((j & (j << 1)) == 0)) {
+                        if (i == 0) {
+                            dp[i][j] = Integer.bitCount(j);
+                        } else {
+                            for (int k = 0; k < stateSize; k++) {
+                                if (((k << 1) & j) == 0 && ((j << 1) & k) == 0 && dp[i - 1][k] != -1) {
+                                    dp[i][j] = Math.max(dp[i][j], dp[i - 1][k] + Integer.bitCount(j));
+                                }
+                            }
+                        }
+                        ans = Math.max(ans, dp[i][j]);
+                    }
+                }
+            }
+            return ans;
+        }
+    }
+}
diff --git a/src/test/java/com/fishercoder/_1349Test.java b/src/test/java/com/fishercoder/_1349Test.java
@@ -0,0 +1,28 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._1349;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _1349Test {
+    private static _1349.Solution1 solution1;
+    private static char[][] seats;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1349.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        seats = new char[][]{
+                {'#', '.', '#', '#', '.', '#'},
+                {'.', '#', '#', '#', '#', '.'},
+                {'#', '.', '#', '#', '.', '#'}
+        };
+        assertEquals(4, solution1.maxStudents(seats));
+    }
+
+}
