本题只能用按小猫枚举来dfs
思路：
1，小猫加入到老的缆车
2，小猫加入到新的缆车

一开始我按缆车来枚举， 其实枚举不到最小值。

代码

import java.io.*;
class Main{
    static int N = 20, n, ans;
    static int w;
    static int[] a = new int[N], groupNum = new int[N];
    static BufferedReader read = new BufferedReader(new InputStreamReader(System.in));
    public static void main(String[] args ) throws Exception{
        String[] ss = read.readLine().split(" ");
        n = Integer.valueOf(ss[0]);
        ans = n;
        w = Integer.valueOf(ss[1]);
        for(int i = 0; i < n; i++){
            a[i] = Integer.valueOf(read.readLine());
        }
        dfs(0, 0, 0);
        System.out.println(ans);

    }

    //按猫枚举
    public static void dfs(int cur, int totalCnt, int maxGroup){
        if(totalCnt == n) {
            ans = Math.min(ans, maxGroup);
        }
        if(maxGroup >= ans || cur >= n) return;

        //加入之前的组
        for(int i = 1; i <= maxGroup; i++){
            int nw = groupNum[i] + a[cur];
            if(nw <= w){
                groupNum[i] = nw;
                dfs(cur + 1, totalCnt + 1, maxGroup);
                groupNum[i] -= a[cur];
            }
        }

        //加入到新建的组
        groupNum[maxGroup + 1] += a[cur];
        dfs(cur + 1, totalCnt + 1, maxGroup + 1);
        groupNum[maxGroup + 1] -= a[cur];

    }
}