Added matrix color

Author: FreeTymeKiyan

Other/MatrixColor.java

@@ -0,0 +1,73 @@
+import java.util.*;
+
+/**
+ * Given a matrix with each grid a color type. Start from a random point, find 
+ * the perimeter of the region of the same color. 
+ * 
+ * Tags: BFS
+ */
+class MatrixColor {
+    public static void main(String[] args) {
+        MatrixColor m = new MatrixColor();
+        int[][] mat = {
+            {2, 2, 1, 2},
+            {2, 2, 1, 2},
+            {2, 1, 1, 2},
+            {2, 2, 1, 2}, 
+        };
+        System.out.println(m.findPerimeter(mat, 0, 2));
+        System.out.println(m.findPerimeter(mat, 0, 1));
+        System.out.println(m.findPerimeter(mat, 0, 3));
+    }
+    
+    /**
+     * BFS
+     * Add the start point to a queue, and set it as visited
+     * Convert 2d coordinate to 1d integer and store it in queue
+     * While the queue is not empty, get an integer from the queue
+     * Convert it back to 2d and search the 4 cells around it
+     * If within board, and not visited, add it to queue and set visited
+     * If not same color, add edge count
+     * If not within board, add edge count
+     */
+    public int findPerimeter(int[][] mat, int x, int y) {
+        if (mat == null || mat.length == 0 || mat[0].length == 0) return 0;
+        
+        Queue<Integer> q = new LinkedList<Integer>();
+        int m = mat.length;
+        int n = mat[0].length;
+        boolean[][] visited = new boolean[m][n];
+        int[][] dir = {{-1, 0}, {0, 1}, {1, 0}, {0, -1}};
+        
+        q.add(x * n + y);
+        visited[x][y] = true;
+        int perimeter = 0;
+        while (!q.isEmpty()) {
+            int size = q.size();
+            for (int i = 0; i < size; i++) {
+                int pos = q.poll();
+                int curX = pos / n;
+                int curY = pos % n;
+                // update perimeter
+                // System.out.println("curX: " + curX + " curY: " + curY);
+                int count = 0;
+                for (int[] d : dir) {
+                    int nX = curX + d[0];
+                    int nY = curY + d[1];
+                    if (nX >= 0 && nX < m && nY >= 0 && nY < n) {
+                        if (mat[nX][nY] == mat[x][y]) {
+                            if (!visited[nX][nY]) {
+                                q.add(nX * n + nY);
+                                visited[nX][nY] = true;
+                            }
+                        } else count++;
+                    }
+                    else count++;
+                }
+                perimeter += count;
+                // System.out.println("count: " + count + " p: " + perimeter);
+            }
+        }
+        return perimeter;
+    }
+}