add 533

Author: fishercoder1534

README.md

@@ -59,6 +59,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |537|[Complex Number Multiplication](https://leetcode.com/problems/complex-number-multiplication/)|[Solution](../master/src/main/java/com/fishercoder/solutions/ComplexNumberMultiplication.java) | O(1) |O(1) | Medium | Math, String
 |536|[Construct Binary Tree from String](https://leetcode.com/problems/construct-binary-tree-from-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/ConstructBinaryTreefromString.java) | O(n) |O(h) | Medium | Recursion
 |535|[Encode and Decode TinyURL](https://leetcode.com/problems/encode-and-decode-tinyurl/)|[Solution](../master/src/main/java/com/fishercoder/solutions/EncodeandDecodeTinyURL.java) | O(1) |O(n) | Medium | Design
+|533|[Lonely Pixel II](https://leetcode.com/problems/lonely-pixel-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_533.java) | O(m*n) |O(m) (m is number of rows) | Medium | HashMap
 |532|[K-diff Pairs in an Array](https://leetcode.com/problems/k-diff-pairs-in-an-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/KdiffPairsinanArray.java) | O(n) |O(n) | Easy | HashMap
 |531|[Lonely Pixel I](https://leetcode.com/problems/lonely-pixel-i/)|[Solution](../master/src/main/java/com/fishercoder/solutions/LonelyPixelI.java) | O(m*n) |O(1) | Medium | 
 |530|[Minimum Absolute Difference in BST](https://leetcode.com/problems/minimum-absolute-difference-in-bst/)|[Solution](../master/src/main/java/com/fishercoder/solutions/MinimumAbsoluteDifferenceinBST.java) | O(n) |O(n) | Easy| DFS

src/main/java/com/fishercoder/solutions/_533.java

@@ -37,69 +37,47 @@
  The range of width and height of the input 2D array is [1,200].
  */
 public class _533 {
-
+    /**Credit: https://discuss.leetcode.com/topic/81686/verbose-java-o-m-n-solution-hashmap/5
+     *
+     * This program is very well designed to do things:
+     * 1. it scans the entire matrix once, but does two things in this scan:
+     * first it records an array of cols that keeps count of how many 'B' are there in each column;
+     * second, at the end of traversing each column, it puts this entire row as the key into a HashMap
+     * when there N number of 'B's in this row.
+     *
+     * 2. then we could go through the HashMap keyset:
+     * if one row has N number of 'B's, we go through this row's each column to see if any element in this row is 'B' and also that element's column has N 'B's*/
     public int findBlackPixel(char[][] picture, int N) {
-        Set<Integer> rows = new HashSet<>();
-        Set<Integer> cols = new HashSet<>();
+        if (picture == null || picture.length == 0 || picture[0].length == 0) return 0;
         int m = picture.length;
         int n = picture[0].length;
+        int[] cols = new int[n];
+        Map<String, Integer> map = new HashMap<>();
+        StringBuilder stringBuilder = new StringBuilder();
         for (int i = 0; i < m; i++) {
-            int blackPixelRowCount = 0;
+            int count  = 0;
             for (int j = 0; j < n; j++) {
-                if (picture[i][j] == 'B') blackPixelRowCount++;
-            }
-            if (blackPixelRowCount == N) rows.add(i);
-        }
-
-        for (int j = 0; j < n; j++) {
-            int blackPixelColCount = 0;
-            for (int i = 0; i < m; i++) {
-                if (picture[i][j] == 'B') blackPixelColCount++;
-            }
-            if (blackPixelColCount == N) cols.add(j);
-        }
-
-        if (!cols.isEmpty()) {
-            Iterator<Integer> colIterator = cols.iterator();
-            int colNumber = colIterator.next();
-            Iterator<Integer> rowIterator = rows.iterator();
-            int compareRowNumber = -1;
-            Set<Integer> rowsThatHaveBlackAtThisCol = new HashSet<>();
-            boolean firstTime = true;
-            while (rowIterator.hasNext()) {
-                int rowNumber = rowIterator.next();
-                if (picture[rowNumber][colNumber] == 'B' && firstTime) {
-                    compareRowNumber = rowNumber;
-                    firstTime = false;
-                } else if (picture[rowNumber][colNumber] == 'B') {
-                    rowsThatHaveBlackAtThisCol.add(rowNumber);
+                if (picture[i][j] == 'B') {
+                    count++;
+                    cols[j]++;
                 }
+                stringBuilder.append(picture[i][j]);
             }
-            if (compareRowNumber == -1) return 0;
-            List<Integer> candidateRows = new ArrayList<>();
-            Iterator<Integer> iterator = rowsThatHaveBlackAtThisCol.iterator();
-            while (iterator.hasNext()) {
-                int row = iterator.next();
-                if (Arrays.equals(picture[row], picture[compareRowNumber])){
-                    candidateRows.add(row);
-                }
+            if (count == N) {
+                /**we use this entire row string as key for the map*/
+                map.put(stringBuilder.toString(), map.getOrDefault(stringBuilder.toString(), 0) + 1);
             }
-            if (candidateRows.size() == 0) return 0;
-
-            candidateRows.add(compareRowNumber);
+            stringBuilder.setLength(0);
+        }
 
-            colIterator = cols.iterator();
-            int result = 0;
-            for (int i = 0; i < candidateRows.size(); i++) {
-                for (int j = 0; j < n; j++) {
-                    if (cols.contains(j) && picture[i][j] == 'B') {
-                        result++;
-                    }
-                }
+        int answer = 0;
+        for (String key : map.keySet()) {
+            if (map.get(key) != N) continue;
+            for (int i = 0; i < n; i++) {
+                if (key.charAt(i) == 'B' && cols[i] == N) answer += N;
             }
-            return result;
         }
-        return 0;
+        return answer;
     }
 
 }

src/test/java/com/fishercoder/_533Test.java

@@ -2,7 +2,6 @@
 
 import com.fishercoder.solutions._533;
 import org.junit.BeforeClass;
-import org.junit.Ignore;
 import org.junit.Test;
 
 import static org.junit.Assert.assertEquals;
@@ -29,9 +28,9 @@ public void test1(){
         assertEquals(6, test.findBlackPixel(picture, 3));
     }
 
-//    @Test
-//    public void test2(){
-//        picture = new char[][]{{'B'}};
-//        assertEquals(1, test.findBlackPixel(picture, 1));
-//    }
+    @Test
+    public void test2(){
+        picture = new char[][]{{'B'}};
+        assertEquals(1, test.findBlackPixel(picture, 1));
+    }
 }