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

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair<int, int> ii;

int main()
{
    ll n;
    scanf("%lld", &n);

    map<int, int> cnt;
    for (int i = 0; i < n; i++) {
        int num;
        scanf("%d", &num);
        cnt[num]++;
    }

    int val[cnt.size() + 1], pre[cnt.size() + 1];
    val[0] = pre[0] = 0;
    int idx = 1;
    for (auto i : cnt)
        val[idx] = i.first, pre[idx] = pre[idx - 1] + i.second, idx++;

    ll ans = 1LL * n * (n - 1) * (n - 2) / 6; // ...

    for (int i = 1; i < (int)cnt.size() + 1; i++) {
        for (int j = i; j < (int)cnt.size() + 1; j++) {
            if (i == j && cnt[val[i]] == 1) {
                continue;
            }

            int target = val[i] + val[j];
            int lb = lower_bound(val + 1, val + idx, target) - val;
            // don't forget -> cnt[val[i]] * (cnt[val[i]] - 1)
            if (i == j) // what a bug!
                ans -= 1LL * cnt[val[i]] * (cnt[val[i]] - 1) / 2 *
                       (pre[idx - 1] - pre[lb - 1]);
            else
                ans -= 1LL * cnt[val[i]] * cnt[val[j]] * (pre[idx - 1] - pre[lb - 1]);
        }
    }

    printf("%lld\n", ans);

    return 0;
}

 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

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair<int, int> ii;

const int INF = 0x3f;

int main()
{
    int n, m, l;
    scanf("%d %d %d", &n, &m, &l);

    int dp[n][n];
    memset(dp, INF, sizeof(dp));
    for (int i = 0; i < m; i++) {
        int u, v, c;
        scanf("%d %d %d", &u, &v, &c);
        u--, v--;
        dp[u][v] = dp[v][u] = c;
    }

    for (int k = 0; k < n; k++)
        for (int i = 0; i < n; i++)
            for (int j = 0; j < n; j++)
                dp[i][j] = min(dp[i][j], dp[i][k] + dp[k][j]);

    int dp2[n][n];
    memset(dp2, INF, sizeof(dp2));
    for (int i = 0; i < n; i++)
        for (int j = 0; j < n; j++)
            if (dp[i][j] <= l)
                dp2[i][j] = 1;

    for (int k = 0; k < n; k++)
        for (int i = 0; i < n; i++)
            for (int j = 0; j < n; j++)
                dp2[i][j] = min(dp2[i][j], dp2[i][k] + dp2[k][j]);

    int q;
    scanf("%d", &q);
    for (int i = 0; i < q; i++) {
        int u, v;
        scanf("%d %d", &u, &v);
        u--, v--;

        int ans;
        if (dp2[u][v] == 0x3f3f3f3f)
            ans = -1;
        else
            ans = dp2[u][v] - 1;
        printf("%d\n", ans);
    }

    return 0;
}