LeetCode --- 547. 朋友圈

• LeetCode链接：547. 朋友圈

• 解法1：深度优先搜索

class Solution {
    public int findCircleNum(int[][] M) {
        boolean[] visited = new boolean[M.length];
        int count = 0;
        for (int i = 0; i < M.length; i++) {
            if (!visited[i]) {
                dfs(M, visited, i);
                count++;
            }
        }
        return count;
    }
    private void dfs(int[][] M, boolean[] visited, int i) {
        for (int j = 0; j < M.length; j++) {
            if(M[i][j] == 1 && !visited[j]) {
                visited[j] = true;
                dfs(M, visited, j);
            }
        }
    }
}

• 解法2：并查集

class Solution {
    public int findCircleNum(int[][] M) {
        UF uf = new UF(M.length);
        for (int i = 0; i < M.length; i++) {
            for (int j = 0; j < i; j++) {
                if (M[i][j] == 1) {
                    uf.union(i,j);
                }
            }
        }
        return uf.count();
    }
    class UF {
        private int[] parents;// 树
        private int[] ranks;  // 树高
        private int count;  // 连通图个数
        public UF(int capacity) {
            parents = new int[capacity];
            ranks = new int[capacity];
            count = capacity;
            for (int i = 0; i < capacity; i++) {
                parents[i] = i;
                ranks[i] = 1;
            }
        }
        public void union(int v1, int v2) {
            int p1 = find(v1);
            int p2 = find(v2);
            if (p1 == p2) return;

            if (ranks[p1] < ranks[p2]) {
                parents[p1] = p2;
            } else if (ranks[p1] > ranks[p2]) {
                parents[p2] = p1;
            } else {
                parents[p1] = p2;
                ranks[p2]++;
            }
            count--;
        }
        public int find(int v) {
            while (parents[v] != v) {
                parents[v] = parents[parents[v]];
                v = parents[v];
            }
            return v;
        }
        int count() {
        	return count;
        }
    }
}