update

poj/1190.birthday-cake/main.cc

@@ -1,3 +1,5 @@
+#include <algorithm>
+#include <cmath>
 #include <cstdio>
 #include <cstring>
 
@@ -7,20 +9,48 @@ const int N = 10000;
 const int M = 20;
 const int INF = 1 << 30;
 
-int n, m;
-int min_area;
+int n, m, min_area = INF;
 
-int min_v[M + 1];
-int min_a[M + 1];
+int min_v[M + 1]; // Min v required for i layers cake
+int min_a[M + 1]; // Min side area required
+
+int maxv_for_lrh(int l, int r, int h) { // Max v for given l, r and h
+  int v = 0;
+  for (int i = 0; i < l; i++) v += (r - i) * (r - i) * (h - i);
+  return v;
+}
 
 void dfs(int l, int v, int area, int r, int h) {
+  if (l == 0) {
+    if (v) return;
+    min_area = min(min_area, area);
+    return;
+  }
+  if (v <= 0) return;
+  if (v < min_v[l]) return;
+  if (min_area <= area + min_a[l]) return;
+  if (r < l || h < l) return;
+  if (maxv_for_lrh(l, r, h) < v) return;
+  for (int nr = r; l <= nr; nr--) {
+    if (l == m) area = nr * nr;  // The area of bottom
+    for (int nh = h; l <= nh; nh--)
+      dfs(l - 1, v - nr * nr * nh, area + 2 * nr * nh, nr - 1, nh - 1);
+  }
 }
 
 int main() {
   scanf("%d %d", &n, &m);
-  for (int i = m; 0 < i; i--) {
+  min_v[0] = 0;
+  min_a[0] = 0;
+  for (int i = 1; i <= m; i++) {
+    min_v[i] = min_v[i - 1] + i * i * i;
+    min_a[i] = min_a[i - 1] + 2 * i * i;
+  }
+  if (min_v[m] <= n) { // Max h and r for bottom layer
+    int max_h = (n - min_v[m - 1]) / (m * m) + 1;
+    int max_r = sqrt(double(n - min_v[m - 1]) / m) + 1;
+    dfs(m, n, 0, max_r, max_h);
   }
-  min_area = INF;
   if (min_area == INF)
     printf("0\n");
   else