[luoguP2854] [USACO06DEC]牛的过山车Cow Roller Coaster(DP + sort)
先按照起点 sort 一遍。
这样每一个点的只由前面的点决定。
f[i][j] 表示终点为 i,花费 j 的最优解
状态转移就是一个01背包。
——代码
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 #include <cstdio> 2 #include <cstring> 3 #include <iostream> 4 #include <algorithm> 5 6 int L, N, B; 7 int f[10001][1001]; 8 9 inline int read() 10 { 11 int x = 0, f = 1; 12 char ch = getchar(); 13 for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -1; 14 for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - '0'; 15 return x * f; 16 } 17 18 struct node 19 { 20 int x, w, f, c; 21 }p[10001]; 22 23 inline bool cmp(node x, node y) 24 { 25 return x.x < y.x; 26 } 27 28 inline int max(int x, int y) 29 { 30 return x > y ? x : y; 31 } 32 33 int main() 34 { 35 int i, j; 36 L = read(); 37 N = read(); 38 B = read(); 39 for(i = 1; i <= N; i++) 40 { 41 p[i].x = read(); 42 p[i].w = read(); 43 p[i].f = read(); 44 p[i].c = read(); 45 p[i].w += p[i].x; 46 } 47 std::sort(p + 1, p + N + 1, cmp); 48 memset(f, -1, sizeof(f)); 49 for(i = 0; i <= B; i++) f[0][i] = 0; 50 for(i = 1; i <= N; i++) 51 for(j = B; j >= p[i].c; j--) 52 if(f[p[i].x][j - p[i].c] ^ -1) 53 f[p[i].w][j] = max(f[p[i].w][j], f[p[i].x][j - p[i].c] + p[i].f); 54 printf("%d\n", f[L][B]); 55 return 0; 56 }