国庆七天乐 Day1
国庆这几天都是做比赛，从今天的情况来说，感觉我还是弱了一点，有些该出的题没做出来，模拟题做得
比较少，该考虑的情况没有考虑，所以E题写了一半，脑子就乱了没写下去，交给了队友。有一种感觉是
学了的东西用不上，或者说不会用，还有好多东西没学。
POJ 3311
Hie with the Pie
这道题其实隽遒学弟的思路没有错，先floyd求出任意两点间的最短路，然后就是旅行商问题（哈密顿回路），
也可以说是状态压缩DP。最多一共就2的11次方乘以10种状态，用f[i][j]表示第i种状态处于j点的最小代价，
我们要求的就是f[(1 <<(n + 1) - 1)[0],从零点出发回到零点。
#include <stdio.h> #include <string.h> #include <stdlib.h> #include <algorithm> using namespace std; const int MAXN = 15; int d[MAXN][MAXN], f[1 << MAXN][MAXN]; int n; void ReadGraph() { for(int i = 0; i <= n; i ++) for(int j = 0; j <= n; j ++) { scanf("%d", &d[i][j]); } } void floyd() { for(int k = 0; k <= n; k ++) for(int i = 0; i <= n; i ++) for(int j = 0; j <= n; j ++) { if(d[i][j] > d[i][k] + d[k][j]) d[i][j] = d[i][k] + d[k][j]; } } void dp() { int i, j, k; memset(f, -1, sizeof f); f[1][0] = 0; for(i = 1; i <= (1 << (n + 1)); i ++) { i = i | 1; for(j = 0; j <= n; j ++) { if(f[i][j] != -1) { for(k = 0; k <= n; k ++) { if(k != j && (f[(1 << k) | i][k] == -1 || f[(1 << k) | i][k] > f[i][j] + d[j][k])) f[ (1 << k) | i][k] = f[i][j] + d[j][k]; } } } } printf("%d\n", f[(1 << (n + 1)) - 1][0]); } int main() { while(scanf("%d", &n), n) { ReadGraph(); floyd(); dp(); } return 0; }
POJ 3316
Snakes on a Plane
这道题当时没看明白，比赛后才理解了题意，我的理解是求出格子中不能变长的贪食蛇的个数。
#include <stdio.h> #include <string.h> #include <stdlib.h> const int MAXN = 205; const int dx[] = {1, -1, 0, 0}; const int dy[] = {0, 0, 1, -1}; char g[MAXN][MAXN]; int r, c; void ReadGraph() { char str[MAXN]; for(int i = 0; i < r; i ++) { scanf("%s", str); for(int j = 0; j < c; j ++) { g[i][j] = str[j]; } } } void mark(int a, int b) { g[a][b] = '2'; for(int i = 0; i < 4; i ++) { int nx = a + dx[i], ny = b + dy[i]; if(nx >= 0 && nx < r && ny >= 0 && ny < c && g[nx][ny] == '1') { mark(nx, ny); } } } int count(int a, int b) { int cnt = 0; for(int i = 0; i < 4; i ++) { int nx = a + dx[i], ny = b + dy[i]; if(nx >= 0 && nx < r && ny >= 0 && ny < c && g[nx][ny] != '0') { cnt ++; } } return cnt; } bool IfExtend(int a, int b) { for(int i = 0; i < 4; i ++) { int nx = a + dx[i], ny = b + dy[i]; if(nx >= 0 && nx < r && ny >= 0 && ny < c && g[nx][ny] == '0') { if(count(nx, ny) == 1) return false; } } return true; } bool IsAnEnd(int a, int b){ if((count(a, b) == 0 || count(a, b) == 1)){ if(IfExtend(a, b)){ return true; } else{ mark(a, b); return false; } } else return false; } bool check(int a, int b){ int neighbors = count(a, b); if(neighbors == 1 || neighbors == 0) { g[a][b] = '2'; return IfExtend(a, b); } if( neighbors > 2) { mark(a, b); return false; } g[a][b] = '2'; for(int i = 0; i < 4; i ++) { int nx = a + dx[i], ny = b + dy[i]; if(nx >= 0 && nx < r && ny >= 0 && ny < c && g[nx][ny] == '1') { return check(nx, ny); } } } bool startSnake(int a, int b){ int neighbors = count(a, b); if(count(a, b) == 0) return true; g[a][b] = '3'; for(int i = 0; i < 4; i ++) { int nx = a + dx[i], ny = b + dy[i]; if(nx >= 0 && nx < r && ny >= 0 && ny < c && g[nx][ny] == '1') { return check(nx, ny); } } } int calc(){ int noSnakes = 0; for(int i = 0; i < r; i ++) for(int j = 0; j < c; j ++){ if(g[i][j] == '1'){ if(IsAnEnd(i, j)){ if(startSnake(i, j)){ noSnakes++; } mark(i,j); } } } return noSnakes; } int main() { while(scanf("%d%d", &r, &c), r + c) { ReadGraph(); printf("%d\n", calc()); } return 0; }