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注意特例：
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//my
///i562
class Solution {
public:
int backPackIV(vector<int> &A, int m) {
int ss = A.size();
vector<vector<int>> dp(ss + 1, vector<int>(m + 1, 0));
dp[0][0] = 1;
for (int i = 1; i <= ss; i++) {
for (int j = 0; j <= m; j++) {
int k = 0;
while (k * A[i - 1] <= j) {
dp[i][j] += dp[i - 1][j - A[i - 1] * k];
k += 1;
}
} // for j
} // for i
return dp[ss][m];
}
};
