我从网上查找资料学习这个知识的，不懂的地方是当判断物品既不是01背包，也不是完全背包时，之后的语句意思就分析不清楚了。我把别人的代码写下来：

题目大意：给你N（1 ≤ N ≤ 100）种钞票以及拥有的张数，以及一个给定的值M（1 ≤ M ≤ 100,000 ）。你需要统计出用这些钞票能够凑出来的钱数，在1 - M的范围中有多少个。

 for (i = 1; i <= n; i++)
        {
            maxi = w[i] * s[i];
            if (s[i] == 1)
            {
                for (j = m; j >= w[i]; j--)
                    dyna[j] = max(dyna[j], dyna[j - w[i]]);
            }
            else if (maxi < m)
            {
                for (j = 0; j < w[i]; j++)
                {
                    head = tail = 0;
                    for (k = j; k <= m; k += w[i])
                    {
                        if (tail != head) { if (k - pl[head] > maxi) head++; }
                        if (dyna[k])
                        {
                            dqueue[tail] = dyna[k];
                            pl[tail] = k; tail++;
                        }
                        else if (tail != head) dyna[k] = 1;
                    }
                }
            }
            else
            {
                for (j = w[i]; j <= m; j++)
                    dyna[j] = max(dyna[j], dyna[j - w[i]]);
            }
        }

每个变量的意思：数组dyna就是DP的那个数组了，maxi变量用于判断物品属于完全背包，还是多重背包。head跟tail用来指示队列的头和尾。

不懂的代码就是
for (j = 0; j < w[i]; j++)
                {
                    head = tail = 0;
                    for (k = j; k <= m; k += w[i])
                    {
                        if (tail != head) { if (k - pl[head] > maxi) head++; }
                        if (dyna[k])
                        {
                            dqueue[tail] = dyna[k];
                            pl[tail] = k; tail++;
                        }
                        else if (tail != head) dyna[k] = 1;
                    }
                }
两个for循环不懂

为什么这样循环怎样不懂