Sicily 1321. Robot

Dijkstra算法，但是由于是网格的缘故，在寻找最短路径时很费时，直接使用会TLE，必须使用优先队列才可以AC。另外也可以用宽搜，但要保证路程必须是最短的 （以往宽搜一般是访问过就不访问了，而在这里用，若新的访问能够使得访问该点的路程变短的话，就必须重新访问）。鉴于宽搜必须全部访问完毕才能够得到最优结果，不同于利用贪心算法的Dijkstra算法可以保证每个子过程都是最优的，所以宽搜不能因为目标节点被访问过就输出结果，而Dijkstra却可以。所以在这点上Dijkstra更有优势。

Run Time: 0.01sec

Run Memory: 304KB

Code length: 1573Bytes

SubmitTime: 2012-01-06 16:52:20

// Problem#: 1321
// Submission#: 1177427
// The source code is licensed under Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License
// URI: http://creativecommons.org/licenses/by-nc-sa/3.0/ // All Copyright reserved by Informatic Lab of Sun Yat-sen University
#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;

struct Path {
int i, j;
int dist;
Path( int a, int b, int c ) { i = a; j = b; dist = c; }
friend bool operator < ( const Path &p1, const Path &p2 ) { return p1.dist > p2.dist; }
};

int dirt[ 4 ][ 2 ] = { { -1, 0 }, { 0, 1 }, { 1, 0 }, { 0, -1 } };

int main()
{
int T;
int row, column;
int si, sj, ti, tj;
int i, j, k;
int grid[ 101 ][ 101 ];
bool included[ 101 ][ 101 ];

scanf( "%d", &T );
while ( T-- ) {
priority_queue<Path> q;
scanf( "%d%d", &row, &column );
for ( i = 1; i <= row; i++ ) {
for ( j = 1; j <= column; j++ )
scanf( "%d", &grid[ i ][ j ] );
}
scanf( "%d%d%d%d", &si, &sj, &ti, &tj );

memset( included, false, sizeof( included ) );
included[ si ][ sj ] = true;
Path add = Path( si, sj, grid[ si ][ sj ] );
while ( !included[ ti ][ tj ] ) {
for ( k = 0; k < 4; k++ ) {
i = add.i + dirt[ k ][ 0 ];
j = add.j + dirt[ k ][ 1 ];
if ( i >= 1 && i <= row && j >= 1 && j <= column && !included[ i ][ j ] ) {
q.push( Path( i, j, add.dist + grid[ i ][ j ] ) );
}
}

add = q.top();
while ( included[ add.i ][ add.j ] ) {
q.pop();
add = q.top();
}
included[ add.i ][ add.j ] = true;
}
printf( "%d\n",add.dist );
}

return 0;

}