feat(leetcode): add No.547

Author: mickey0524

547.Friend-Circles.java

@@ -0,0 +1,40 @@
+// https://leetcode.com/problems/friend-circles/
+//
+// algorithms
+// Medium (53.54%)
+// Total Accepted: 84,688
+// Total Submissions: 158,175
+// beats 100.0% of java submissions
+
+class Solution {
+    public int findCircleNum(int[][] M) {
+        if (M == null) {
+            return 0;
+        }
+        int n = M.length;
+        if (n == 0) {
+            return 0;
+        }
+
+        int flag = 2;
+        for (int i = 0; i < n; i++) {
+            if (M[i][i] == 1) {
+                recursive(M, i, flag);
+                flag++;
+            }
+        }
+
+        return flag - 2;
+    }
+
+    public void recursive(int[][] M, int idx, int flag) {
+        int n = M.length;
+        M[idx][idx] = flag;
+
+        for (int i = 0; i < n; i++) {
+            if (M[idx][i] == 1 && M[i][i] == 1) {
+                recursive(M, i, flag);
+            }
+        }
+    }
+}