/**
     * 错误case  如果K>N，a[i]数组溢出
     *
     * for(int i=2;i<=K;i++){
     *             a[i] = (a[i-1]*2)%magic;
     *         }
     *         for(int i=K+1;i<=N;i++){
     *                 a[i] = (a[i-1]*2 - a[i-K-1])%magic;
     *         }
     */
    for(int i=2;i<=N;i++){
        if(i<=K){
            a[i] = (a[i-1]*2)%magic;
        } else {
            a[i] = (a[i-1]*2 - a[i-K-1])%magic;
        }

    }