public int  jump(int [] A){
        int minStep = 0;  //当前所需要的步数
        int distance =0;  //当前步数所能到达的最远距离
        int current =0;   // 下一步能到达的最远距离
        for (int i=0; i< A.length ;i++) {
            if(i > distance){
                ++minStep;
                distance = current;
            }
            current = Math.max(current,i+A[i]);
        }
        return minStep;

    }