class Solution {
    public int addRungs(int[] rungs, int dist) {
        int len = rungs.length;
        int res = 0;
        if(rungs == null || len == 0)
            return 0;
        if(rungs[0] > dist && len >= 1 && rungs[0] % dist == 0){        
        //余0时结果会不一样，需减去一个dist
            res = (rungs[0] - dist) / dist;
        }
        else if(rungs[0] > dist && len >= 1){
            res = rungs[0] / dist;
        }
        for(int i = 1; i < len; i++){
            if(rungs[i] - rungs[i - 1] > dist && (rungs[i] - rungs[i - 1]) % dist == 0){
	             //余0时结果会不一样，需减去一个dist
                res = res + (rungs[i] - rungs[i - 1] - dist) / dist;
            }
            else if(rungs[i] - rungs[i - 1] > dist){
                res = res + (rungs[i] - rungs[i - 1]) / dist;
            }
        }
        return res;
    }
}