uva 1078 - Steam Roller（最短路）

题目链接：uva 1078 - Steam Roller

建图，将一个点拆成8个点，分别是4个方向，以及入边是否加倍。然后做最短路。

#include <cstdio>#include <cstring>#include <vector>#include <queue>#include <algorithm>using namespace std;const int maxn = 105;const int inf = 0x3f3f3f3f;const int UP = 0, LEFT = 1, DOWN = 2, RIGHT = 3;const int inv[] = {2, 3, 0, 1};const int dr[] = {-1, 0, 1, 0};const int dc[] = {0, -1, 0, 1};int R, C, grid[maxn][maxn][4];int N, id[maxn][maxn][4][2];inline int readint() { int x; scanf("%d", &x); return x; }inline int ID (int r, int c, int d, int doubled) {int& x = id[r][c][d][doubled];if (x == 0) x = ++N;return x;}inline bool cango(int r, int c, int d) {if (r < 0 || r >= R || c < 0 || c >= C) return false;return grid[r][c][d] > 0;}struct Dijkstra {struct Edge {int u, v, w;Edge (int u = 0, int v = 0, int w = 0): u(u), v(v), w(w) {}};struct State {int u, d;State(int u = 0, int d = 0): u(u), d(d) {}bool operator < (const State& u) const { return d > u.d; }};int n, m, d[maxn * maxn * 10], v[maxn * maxn * 10];vector<Edge> edges;vector<int> G[maxn * maxn * 10];void init (int n) {this->n = n;edges.clear();for (int i = 0; i < n; i++) G[i].clear();}void addEdge(int u, int v, int w) {edges.push_back(Edge(u, v, w));m = edges.size();G[u].push_back(m-1);}void dijkstra(int s) {memset(d, inf, sizeof(d));memset(v, 0, sizeof(v));d[s] = 0;priority_queue<State> Q;Q.push(State(s, d[s]));while(!Q.empty()) {int u = Q.top().u;Q.pop();if (v[u]) continue;v[u] = 1;for (int i = 0; i < G[u].size(); i++) {Edge& e = edges[G[u][i]];if (d[e.v] > d[u] + e.w) {d[e.v] = d[u] + e.w;Q.push(State(e.v, d[e.v]));}}}}}solver;void init () {N = 0;memset(id, 0, sizeof(id));memset(grid, 0, sizeof(grid));solver.init(R * C * 8 + 1);for (int r = 0; r < R; r++) {for (int c = 0; c < C-1; c++)grid[r][c][RIGHT] = grid[r][c+1][LEFT] = readint();if (r != R-1) for (int c = 0; c < C; c++)grid[r][c][DOWN] = grid[r+1][c][UP] = readint();}}int main () {int cas = 0, r1, c1, r2, c2;while (scanf("%d%d%d%d%d%d", &R, &C, &r1, &c1, &r2, &c2) == 6 && R) {r1--, c1--, r2--, c2--;init();for (int d = 0; d < 4; d++) if(cango(r1, c1, d))solver.addEdge(0, ID(r1+dr[d], c1+dc[d], d, 1), grid[r1][c1][d]* 2);for (int r = 0; r < R; r++) {for (int c = 0; c < C; c++) {for (int dir = 0; dir < 4; dir++) if (cango(r, c, inv[dir])) {for (int newdir = 0; newdir < 4; newdir++) if (cango(r, c, newdir)) {for (int doubled = 0; doubled < 2; doubled++) {int newr = r + dr[newdir];int newc = c + dc[newdir];int v = grid[r][c][newdir], newdoubled = 0;if (dir != newdir) {if (!doubled) v += grid[r][c][inv[dir]];newdoubled = 1; v += grid[r][c][newdir];}solver.addEdge(ID(r, c, dir, doubled), ID(newr, newc, newdir, newdoubled), v);}}}}}solver.dijkstra(0);int ans = inf;for (int d = 0; d < 4; d++) if (cango(r2, c2, inv[d]))for (int doubled = 0; doubled < 2; doubled++) {int v = solver.d[ID(r2, c2, d, doubled)];if (!doubled) v += grid[r2][c2][inv[d]];ans = min(ans, v);}printf("Case %d: ", ++cas);if (ans == inf) printf("Impossible\n");else printf("%d\n", ans);}return 0;}