Add solution #531

Author: JoshCrozier

README.md

@@ -517,6 +517,7 @@
 528|[Random Pick with Weight](./solutions/0528-random-pick-with-weight.js)|Medium|
 529|[Minesweeper](./solutions/0529-minesweeper.js)|Medium|
 530|[Minimum Absolute Difference in BST](./solutions/0530-minimum-absolute-difference-in-bst.js)|Easy|
+531|[Lonely Pixel I](./solutions/0531-lonely-pixel-i.js)|Medium|
 532|[K-diff Pairs in an Array](./solutions/0532-k-diff-pairs-in-an-array.js)|Medium|
 535|[Encode and Decode TinyURL](./solutions/0535-encode-and-decode-tinyurl.js)|Medium|
 537|[Complex Number Multiplication](./solutions/0537-complex-number-multiplication.js)|Medium|

solutions/0531-lonely-pixel-i.js

@@ -0,0 +1,42 @@
+/**
+ * 531. Lonely Pixel I
+ * https://leetcode.com/problems/lonely-pixel-i/
+ * Difficulty: Medium
+ *
+ * Given an m x n picture consisting of black 'B' and white 'W' pixels, return the number of
+ * black lonely pixels.
+ *
+ * A black lonely pixel is a character 'B' that located at a specific position where the same
+ * row and same column don't have any other black pixels.
+ */
+
+/**
+ * @param {character[][]} picture
+ * @return {number}
+ */
+var findLonelyPixel = function(picture) {
+  const rows = picture.length;
+  const cols = picture[0].length;
+  const rowCounts = new Array(rows).fill(0);
+  const colCounts = new Array(cols).fill(0);
+  let result = 0;
+
+  for (let row = 0; row < rows; row++) {
+    for (let col = 0; col < cols; col++) {
+      if (picture[row][col] === 'B') {
+        rowCounts[row]++;
+        colCounts[col]++;
+      }
+    }
+  }
+
+  for (let row = 0; row < rows; row++) {
+    for (let col = 0; col < cols; col++) {
+      if (picture[row][col] === 'B' && rowCounts[row] === 1 && colCounts[col] === 1) {
+        result++;
+      }
+    }
+  }
+
+  return result;
+};