547 Number of Provinces

Leetcode

There are n cities. Some of them are connected, while some are not. If city a is connected directly with city b, and city b is connected directly with city c, then city a is connected indirectly with city c.

A province is a group of directly or indirectly connected cities and no other cities outside of the group.

You are given an n x n matrix isConnected where isConnected[i][j] = 1 if the ith city and the jth city are directly connected, and isConnected[i][j] = 0 otherwise.

Return the total number of provinces.

Example 1:

Input: isConnected = [[1,1,0],[1,1,0],[0,0,1]]
Output: 2

Example 2:

Input: isConnected = [[1,0,0],[0,1,0],[0,0,1]]
Output: 3

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遍历所有的城市，遇到未标记的城市就对其进行深度优先或广度优先搜索，标记所有的城市，这些是同一个省，记录省数。

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