省份数量——并查集

题目：

代码：

private static int mergeFind(int[][] citysConnected){
        int citys = citysConnected.length;
        int[] head = new int[citys];
        int[] level = new int[citys];
        for (int i =0;i<citys;i++){
            head[i] = i;
            level[i] = 1;
        }
        for (int i =0;i<citys;i++){
            for (int j=i+1;j<citys;j++){
                if (citysConnected[i][j]==1){
                    merge(i,j,head,level);
                }
            }
        }
        int count = 0;
        for (int i=0;i<citys;i++){
            if (head[i]==i){
                count++;
            }
        }
        return count;
    }
    static void merge(int x,int y,int[] head,int[] level){
        int i = find(x,head);
        int j = find(y,head);

        if (i==j){
            return;
        }
        if (level[i]<=level[j]){
            head[i] = j;
        }else {
            head[j] = i;
        }
        if (level[i]==level[j]){
            level[i]++;
            level[j]++;
        }
    }


    private static int find(int x,int[] head){
        if (head[x]==x){
            return x;
        }
        head[x] = find(head[x],head);
        return head[x];
    }