[LEET-531] add 531

Author: fishercoder1534

leetcode-algorithms/README.md

@@ -4,6 +4,7 @@
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
 |535|[Encode and Decode TinyURL](https://leetcode.com/problems/encode-and-decode-tinyurl/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/EncodeandDecodeTinyURL.java) | O(1) |O(n) | Medium | Design
+|531|[Lonely Pixel I](https://leetcode.com/problems/lonely-pixel-i/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/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/leetcode-algorithms/src/main/java/com/stevesun/solutions/MinimumAbsoluteDifferenceinBST.java) | O(n) |O(n) | Easy| DFS
 |529|[Minesweeper](https://leetcode.com/problems/minesweeper/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/Minesweeper.java) | O(m*n) |O(k) | Medium | BFS
 |520|[Detect Capital](https://leetcode.com/problems/detect-capital/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/DetectCapital.java) | O(n) |O(1) | Easy| 

leetcode-algorithms/src/main/java/com/stevesun/solutions/LonelyPixelI.java

@@ -0,0 +1,52 @@
+package com.stevesun.solutions;
+
+/**
+ * Given a picture consisting of black and white pixels, find the number of black lonely pixels.
+
+ The picture is represented by a 2D char array consisting of 'B' and 'W', which means black and white pixels respectively.
+
+ A black lonely pixel is character 'B' that located at a specific position where the same row and same column don't have any other black pixels.
+
+ Example:
+ Input:
+ [['W', 'W', 'B'],
+ ['W', 'B', 'W'],
+ ['B', 'W', 'W']]
+
+ Output: 3
+ Explanation: All the three 'B's are black lonely pixels.
+ Note:
+ The range of width and height of the input 2D array is [1,500].
+ */
+public class LonelyPixelI {
+
+    public int findLonelyPixel(char[][] picture) {
+        int m = picture.length;
+        int n = picture[0].length;
+        int count = 0;
+        for (int i = 0; i < m; i++) {
+            for (int j = 0; j < n; j++) {
+                if (picture[i][j] == 'B' && isLonely(i, j, picture, m, n)) {
+                    count++;
+                }
+            }
+        }
+        return count;
+    }
+
+    private boolean isLonely(int row, int col, char[][] picture, int m, int n) {
+        for (int i = 0; i < m; i++) {
+            if (i != row) {
+                if (picture[i][col] == 'B') return false;
+            }
+        }
+
+        for (int j = 0; j < n; j++) {
+            if (j != col) {
+                if (picture[row][j] == 'B') return false;
+            }
+        }
+        return true;
+    }
+
+}