Twitter OA prepare: Visit element of the array

分析：就是建立一个boolean array来记录array里面每个元素的访问情况，遇到访问过的元素就停止visiting，返回未访问的结点个数

 public int visiting(int[] A, int N) {
     if (A==null || A.length==0) return 0;
     int cur = 0;
     int count = 0;
     boolean[] visited = new boolean[N];
     while (cur>=0 && cur<A.length && !visited[cur]) {
         visited[cur] = true;
         cur = cur + A[cur];
         count++;
     }
     return N-count;
 }