题意
有n个时间段,每个时间段有2节课,最多可以换m次课,概率给出
把校园抽象成无向图,求耗费最小体力值
题解
这是一道期望Dp,f[i][j][k]表示考虑到第i个教室,换了j次,k为0/1,表示这次是否换
分四种情况,具体见代码
调试记录
double的输入提示符是%lf,不是%llf
害老子调了一个小时
#include <cstdio>
#include <algorithm>
#include <cstring>
#define maxn 2005
#define INF 0x3f3f3f3f
using namespace std;
int n, m, v, e;
int c[maxn], d[maxn], dis[305][305];
double f[maxn][maxn][2];
double k[maxn];
void Floyd(){
for (int i = 1; i <= v; i++)
for (int j = 1; j < i; j++)
dis[j][i] = dis[i][j] = INF;
for (int x, y, w, i = 1; i <= e; i++){
scanf("%d%d%d", &x, &y, &w);
dis[x][y] = dis[y][x] = min(dis[x][y], w);
}
for (int k = 1; k <= v; k++){
for (int i = 1; i <= v; i++){
for (int j = 1; j < i; j++)
dis[j][i] = dis[i][j] = min(dis[i][j], dis[i][k] + dis[k][j]);
}
}
}
int main(){
scanf("%d%d%d%d", &n, &m, &v, &e);
for (int i = 1; i <= n; i++) scanf("%d", &c[i]);
for (int i = 1; i <= n; i++) scanf("%d", &d[i]);
for (int i = 1; i <= n; i++) scanf("%lf", &k[i]);
Floyd();
for (int i = 1; i <= n; i++)
for (int j = 0; j <= m; j++)
f[i][j][0] = f[i][j][1] = INF;
f[1][0][0] = 0, f[1][1][1] = 0;
for (int i = 2; i <= n; i++){
double w1 = dis[c[i - 1]][c[i]];
double w2 = dis[d[i - 1]][c[i]] * k[i - 1] + dis[c[i - 1]][c[i]] * (1.0 - k[i - 1]);
double w3 = dis[c[i - 1]][d[i]] * k[i] + dis[c[i - 1]][c[i]] * (1.0 - k[i]);
double w4 = dis[d[i - 1]][d[i]] * k[i - 1] * k[i]
+ dis[d[i - 1]][c[i]] * k[i - 1] * (1.0 - k[i])
+ dis[c[i - 1]][d[i]] * (1.0 - k[i - 1]) * k[i]
+ dis[c[i - 1]][c[i]] * (1.0 - k[i - 1]) * (1.0 - k[i]);
for (int j = 0; j <= min(i, m); j++){
f[i][j][0] = min(f[i - 1][j][0] + w1, f[i - 1][j][1] + w2);
if (j > 0) f[i][j][1] = min(f[i - 1][j - 1][0] + w3, f[i - 1][j - 1][1] + w4);
}
}
double ans = INF;
for (int i = 0; i <= m; i++)
ans = min(ans, (double)min(f[n][i][0], f[n][i][1]));
printf("%0.2lf\n", ans);
return 0;
}