杭电 hdu 1548 A strange lift

好吧，一条小小的贪心搞了我一个半小时，主要是图没有制好，所以屡次WA。同时也没有考虑到 5 1 1 和 5 5 1的情况。两者要分别输出 0 和 -1.

/* THE ROGRAM IS MADE BY PYY */ /*----------------------------------------------------------------------------// URL : http://acm.hdu.edu.cn/showproblem.php?pid=1548 Name : A strange lift Date : Saturday, April 16, 2011 Time Stage : 20:06~21:27 Result: 3829659 2011-04-16 21:26:13 Accepted 1548 46MS 448K 2913 B C++ pyy Test Data: Sample Input 5 1 5 3 3 1 2 5 5 1 1 3 3 1 2 5 5 5 1 3 3 1 2 5 0 Sample Output 3 0 -1 Summary: 此题实际上并不难，由于第一次做有向图，所以移动的方向没有注意到。导致屡次 WA。 就此次做题来说，关键的一点是制图。一定要注意有向图的制法跟无向图是不同的。 并且要重点检查图是否正确。 //----------------------------------------------------------------------------*/ #include <iostream> #include <string.h> #include <stdio.h> using namespace std; const int maxSize = 202, infinite = 0x0f0f0f0f; int floor, minTrip, start, end; int map[maxSize][maxSize], dp[maxSize], jump[maxSize], mark[maxSize]; // 附加函数，用于临时查看数组 void out( int (*arr)[maxSize] ) { int i, j; for( i = 1; i <= floor; i++ ) { for( j = 1; j <= floor; j++ ) cout << arr[i][j] << " "; cout << endl; } } void dijkstra() { int i, j, k; if( start == end ) { minTrip = 0; return ; } memset( mark, 0, sizeof( mark ) ); for( i = 1; i <= floor; i++ ) dp[i] = map[start][i]; for( i = 1; i <= floor; i++ ) { int minPath = infinite; int iminPath = 0; for( j = 1; j <= floor; j++ ) if( !mark[j] && dp[j] < minPath ) { iminPath = j; minPath = dp[j]; } mark[iminPath] = 1; for( j = 1; j <= floor; j++ ) if( !mark[j] && dp[iminPath] + map[iminPath][j] < dp[j] ) dp[j] = dp[iminPath] + map[iminPath][j]; } // 若 dp[end] 的值仍为 infinite 则没有到 end 的路径 if( infinite == dp[end] ) minTrip = -1; else minTrip = dp[end]; } int main() { int i, j, k; while( cin >> floor && floor ) { memset( map, infinite, sizeof( map ) ); cin >> start >> end; for( i = 1; i <= floor; i++ ) { cin >> jump[i]; // cout << endl << i << " " << jump[i] + i << endl; // 这是个有向图，注意 map[i][i+jump[i]] 和 map[i+jump[i]][i] 是不同的。 if( i + jump[i] <= floor ) { map[i][i+jump[i]] = 1; // printf("%d->%d/t", i, i+jump[i] ); } if( i - jump[i] > 0 ) { map[i][i-jump[i]] = 1; // printf("%d->%d", i-jump[i], i ); } // cout << endl; } // out( map ); dijkstra(); cout << minTrip << endl; } return 0; }