new file: P8712.cpp

P8712.cpp

@@ -0,0 +1,34 @@
+#include <bits/stdc++.h>
+#define int long long
+using namespace std;
+int n, k;
+int a[100005];
+int mod[100005][11];
+int ks[100005][11];
+signed main() {
+    scanf("%lld%lld", &n, &k);
+    for (int i = 1; i <= n; ++i) {
+        scanf("%lld", &a[i]);
+        mod[i][0] = a[i] % k;
+        ks[mod[i][0]][0]++;
+        for (int j = 1; j <= 10; ++j) {
+            mod[i][j] = (mod[i][j - 1] * 10) % k;
+            ks[mod[i][j]][j]++;
+        }
+    }
+    int ans = 0;
+    for (int i = 1; i <= n; ++i) { // 作为底部
+        int len, now = a[i];
+        for (len = 0; now; len++, now /= 10)
+            ;
+        int want = (k - mod[i][0]) % k;
+        ans += ks[want][len];
+        if (mod[i][len] == want)
+            ans--;
+    }
+    printf("%lld\n", ans);
+    return 0;
+}
+/*
+计算 *10^i mod k
+*/