meetings

contests/silver/2019/december/meetings/meetings.cpp

@@ -1,15 +1,18 @@
 #include <bits/stdc++.h>
 using namespace std;
 
-#define MAX_N 50000
+#define MAX_N 5e4
+#define pii pair<int, int>
 
 struct Cow
 {
-  int w, x;
-  bool operator<(const Cow& o) { return x < o.x; }
+  int w, x, d;
 };
 
-vector<Cow> leftC, rightC;
+vector<Cow> cows(MAX_N);
+vector<Cow> leftC(MAX_N), rightC(MAX_N);
+vector<pii> poi(MAX_N * 50);
+
 int main()
 {
   ifstream fin("meetings.in");
@@ -18,20 +21,61 @@ int main()
   int N, L;
   fin >> N >> L;
 
-  int w, x, d;
-  for (int i = 0; i < N; ++i) 
+  int numLeft = 0, totalW = 0;
+  for (int i = 0; i < N; ++i)
   {
-    cin >> w >> x >> d;
-    if (d == -1) leftC.push_back({ w, x });
-    else rightC.push_back({ w, x });
+    fin >> cows[i].w >> cows[i].x >> cows[i].d;
+    numLeft += cows[i].d == -1;
+    totalW += cows[i].w;
   }
 
-  sort(leftC.begin(), leftC.end());
-  sort(rightC.begin(), rightC.end());
+  sort(cows.begin(), cows.begin() + N, [](const Cow &a, const Cow &b)
+  { return a.x < b.x; });
 
-  // find T
-  int i, j, T;
-
+  int leftI = 0, rightI = 0;
+  for (int i = 0; i < N; ++i)
+  {
+    if (cows[i].d == -1) leftC[leftI++] = cows[i];
+    else rightC[rightI++] = cows[i];
+  }
+
+  int poiI = 0;
+  for (int i = 0; i < leftI; ++i)
+    poi[poiI++] = {leftC[i].x, cows[i].w};
+
+  for (int i = 0; i < rightI; ++i)
+    poi[poiI++] = {L - rightC[i].x, cows[leftI + i].w};
+
+  sort(poi.begin(), poi.begin() + poiI, [](const pii &a, const pii &b)
+  { return a.first < b.first; });
+
+  int T = -1, w = 0;
+  for (int i = 0; i < poiI; ++i)
+  {
+    w += poi[i].second;
+    if (w * 2 >= totalW)
+    {
+      T = poi[i].first;
+      break;
+    }
+  }
+
+  assert(T != -1);
+
+  int ans = 0;
+  int i = 0, j = 0;
+  for (int l = 0; l < rightI; ++l)
+  {
+    while (i < leftI && leftC[i].x < rightC[l].x)
+      ++i;
+
+    while (j < leftI && leftC[j].x <= rightC[l].x + T * 2)
+      ++j;
+
+    ans += j - i;
+  }
+
+  fout << ans << '\n';
 
   return 0;
-}
+}

contests/silver/2019/december/meetings/meetings.in

@@ -0,0 +1,4 @@
+3 5
+1 1 1
+2 2 -1
+3 3 -1

contests/silver/2019/december/meetings/meetings.out

@@ -0,0 +1 @@
+2