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描述的问题看起来像是来自竞赛的任务。我没有参加任何比赛,也没有任何正在进行的比赛,可能涉及到这个问题。如果有任何一个,我将结束问题以保持公平!
我有一个问题:给定值A的数组A和整数K,将A拆分为正好K个不重叠的连续子数组,这样子数组具有最小和的子数组最大和之间的差异就最小。允许将A沿任意方向旋转任意数量。
考虑一个例子:
输入:A = [5 1 1 1 3 2],K = 3 输出:[5] [1 1 1] [3 2],最大和= 5,最小和= 3,结果= 2
输入:A = [5 1 1 1 3 2],K = 3
输出:[5] [1 1 1] [3 2],最大和= 5,最小和= 3,结果= 2
我有部分工作代码(非常丑陋,我很糟糕,但这并不代表生产质量):
#include <climits> #include <cstdio> #include <cstring> const int max_n = 50; const int max_k = 20; int deps[max_n]; int max (int x, int y) { return x > y ? x : y; } int min (int x, int y) { return x < y ? x : y; } int sum (int a[], int start, int end) { int res = 0; for (int i = start; i <= end; ++i) res += a[i]; return res; } int k_partitioning(int k, int n, int deps[]) { int res = INT_MAX; // consider all possible rotations/shifts for(int offset = 0; offset < n; ++offset) { for(int l_min = 0; l_min < n; ++l_min) { for(int r_min = l_min; r_min < n; ++r_min) { // check minimal sum subarray int min_sum = sum (deps, l_min, r_min); int dp[k][n]; for (int s = 0; s < k; ++s) { for (int q = 0; q < n; ++q) { dp[s][q] = 0; } } // assuming that current sum is a target sum dp[0][r_min-l_min] = min_sum; for(int p = 1; p < k; ++p) { for(int l_max = 0; l_max < n; ++l_max) { for(int r_max = 0; r_max < n; ++r_max) { int max_sum = sum(deps, l_max, r_max); if (max_sum >= min_sum) dp[p][r_max] = max(dp[p-1][l_max], max_sum); } // l_maxs } // r_maxs } // partitions // printing dp // skip incorrect partitioning, when not all K partitions were used if (dp[k-1][n-1] == 0) continue; // update difference res = min (res, dp[k-1][n-1] - min_sum); } // end min sum seg } // start min sum seg //break; } // cuts return res; } int main(int argc, char* argv[]) { int k = 0; scanf("%d", &k); int n = 0; scanf("%d", &n); for (int i = 0; i < n; ++i) { scanf("%d", &deps[i]); } printf ("%d\n", k_partitioning(k, n, deps)); return 0; }
这个想法很简单:假设当前分区具有最小总和,枚举所有可能的最大分区,设置动态编程以生成具有最小值的最大总和,检查差异。总复杂度:O(K * N ^ 4)。
我的问题是它无法通过某些测试,因此无法解决问题。有人可以帮我吗?
测试失败,例如:
N = 4,K = 2,A = [6 13 10 2]
更新
此版本应解决以前的一些问题。首先,它消除了“偏移”上的浪费循环,并仅在l_min循环的末尾添加了数组旋转。其次,我注意到,dp不能用0初始化- 这是最小化任务,因此应使用较大的值进行初始化(取决于问题的常量,此处的max_value已经超出了值域)。最后,间隔不应再重叠- 每个和都排除间隔的左端。但是,它仍然无法产生预期的结果。
#include <climits> #include <cstdio> #include <cstring> const int max_value = 200000; const int max_n = 50; const int max_k = 20; int deps[max_n]; int max (int x, int y) { return x > y ? x : y; } int min (int x, int y) { return x < y ? x : y; } int sum (int a[], int start, int end) { int res = 0; for (int i = start; i <= end; ++i) res += a[i]; return res; } int k_partitioning(int k, int n, int deps[]) { int res = max_value; for(int l_min = 0; l_min < n; ++l_min) { for(int r_min = l_min; r_min < n; ++r_min) { int min_sum = sum (deps, l_min+1, r_min); int dp[k][n]; for (int s = 0; s < k; ++s) { for (int q = 0; q < n; ++q) { dp[s][q] = max_value; } } // assuming that current sum is a target sum dp[0][r_min-l_min] = min_sum; for(int p = 1; p < k; ++p) { for(int l_max = 0; l_max < n; ++l_max) { for(int r_max = l_max; r_max < n; ++r_max) { int max_sum = sum(deps, l_max+1, r_max); if (max_sum >= min_sum) dp[p][r_max] = max(dp[p-1][l_max], max_sum); } // l_maxs } // r_maxs } // partitions // skip incorrect partitioning, when not all K partitions were used if (dp[k-1][n-1] == max_value) continue; // update difference res = min (res, dp[k-1][n-1] - min_sum); } // end min sum seg // rotate an array to consider different starting points int tmp[n]; for (int i = 0; i < n; ++i) { int new_idx = i + n + 1; tmp[new_idx % n] = deps[i]; } for(int i = 0; i < n; ++i) deps[i] = tmp[i]; } // start min sum seg return res; } int main(int argc, char* argv[]) { int k = 0; scanf("%d", &k); int n = 0; scanf("%d", &n); for (int i = 0; i < n; ++i) { scanf("%d", &deps[i]); } printf ("%d\n", k_partitioning(k, n, deps)); return 0; }
好吧,我想我做到了!
想法如下:我们假设最小总和间隔始终从0开始。然后,我们开始从最小间隔的右边界开始枚举最大总和间隔。我们为当前最大间隔构建DP问题,以确定最小最大和。之后,您更新结果并将数组旋转一个。
我的代码在每次迭代中计算电流总和的方式上并不完美。可以预先计算它们,而每次都只对其编制索引。
这段代码可能有一些错误,但是它通过了我的所有测试。
#include <climits> #include <cstdio> #include <cstring> const int max_value = 200000; const int max_n = 50; const int max_k = 20; int deps[max_n]; int max (int x, int y) { return x > y ? x : y; } int min (int x, int y) { return x < y ? x : y; } int sum (int a[], int start, int end) { int res = 0; for (int i = start; i <= end; ++i) res += a[i]; return res; } int k_partitioning(int k, int n, int deps[]) { int res = max_value; for(int offset = 0; offset < n; ++offset) { int l_min = 0; for(int r_min = l_min; r_min < n; ++r_min) { int min_sum = sum (deps, l_min, r_min); int dp[k][n]; for (int s = 0; s < k; ++s) { for (int q = 0; q < n; ++q) { dp[s][q] = max_value; } } // assuming that current sum is a target sum dp[0][r_min-l_min] = min_sum; for(int p = 1; p < k; ++p) { for(int l_max = r_min; l_max < n; ++l_max) { for(int r_max = l_max; r_max < n; ++r_max) { int max_sum = sum(deps, l_max+1, r_max); if (max_sum >= min_sum) { dp[p][r_max] = min(dp[p][r_max], max(dp[p-1][l_max], max_sum)); } } // l_maxs } // r_maxs } // partitions // skip incorrect partitioning, when not all K partitions were used if (dp[k-1][n-1] == max_value) continue; // update difference res = min (res, dp[k-1][n-1] - min_sum); } // end min sum seg int tmp[n]; for (int i = 0; i < n; ++i) { int new_idx = i + n - 1; tmp[new_idx % n] = deps[i]; } for(int i = 0; i < n; ++i) deps[i] = tmp[i]; } // start min sum seg return res; } int main(int argc, char* argv[]) { int k = 0; scanf("%d", &k); int n = 0; scanf("%d", &n); for (int i = 0; i < n; ++i) { scanf("%d", &deps[i]); } printf ("%d\n", k_partitioning(k, n, deps)); return 0; }