四、阅读程序-3

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71

#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>
#define ll long long

int n, m;
std::vector<int> k, p;

inline int mpow(int x, int k) {
    int ans = 1;
    for (; k; k >>= 1, x = x * x) {
        if (k & 1)
            ans = ans * x;
    }
    return ans;
}

std::vector<int> ans1, ans2;
int cnt1, cnt2;

inline void dfs(std::vector<int>& ans, int& cnt, int l, int r, int v) {
    if (l > r) {
        ++cnt;
        ans.push_back(v);
        return;
    }
    for (int i = 1; i <= m; ++i) {
        dfs(ans, cnt, l + 1, r, v + k[l] * mpow(i, p[l]));
    }
    return;
}

std::vector<int> cntans1;

int main() {
    scanf("%d%d", &n, &m);
    k.resize(n + 1);
    p.resize(n + 1);
    for (int i = 1; i <= n; ++i) {
        scanf("%d%d", &k[i], &p[i]);
    }

    dfs(ans1, cnt1, 1, n >> 1, 0);
    dfs(ans2, cnt2, (n >> 1) + 1, n, 0);

    std::sort(ans1.begin(), ans1.end());
    int newcnt1 = 1;
    cntans1.push_back(1);
    for (int i = 1; i < cnt1; ++i) {
        if (ans1[i] == ans1[newcnt1 - 1]) {
            ++cntans1[newcnt1 - 1];
        } else {
            ans1[newcnt1++] = ans1[i];
            cntans1.push_back(1);
        }
    }
    cnt1 = newcnt1;

    std::sort(ans2.begin(), ans2.end());
    int las = 0;
    ll ans = 0;
    for (int i = cnt2 - 1; i >= 0; --i) {
        for (; las < cnt1 && ans1[las] + ans2[i] < 0; ++las)
            ;
        if (las < cnt1 && ans1[las] + ans2[i] == 0)
            ans += cntans1[las];
    }
    printf("%lld\n", ans);
    return 0;
}