题目：

题解：

int change(int amount, int* coins, int coinsSize) {
    int dp[amount + 1];
    bool valid[amount + 1];
    memset(dp, 0, sizeof(dp));
    memset(valid, false, sizeof(valid));
    dp[0] = 1;
    valid[0] = true;
    for (int i = 0; i < coinsSize; i++) {
        for (int j = coins[i]; j <= amount; j++) {
            valid[j] |= valid[j - coins[i]];
        }
    }
    if (!valid[amount])
        return 0;
    for (int i = 0; i < coinsSize; i++) {
        for (int j = coins[i]; j <= amount; j++) {
            dp[j] += dp[j - coins[i]];
        }
    }
    return dp[amount];
}