Algo Project 2

#include <bits/stdc++.h>
using namespace std;

typedef pair<int,int> ii;
#define OO 0x7fffffff
#define S second
#define F first

int dx[] = {1 ,-1 ,0 , 0};
int dy[] = {0 , 0 ,1 ,-1};
const int N = 1e3 + 3e1;

vector< vector< ii > > kColorIdx;
int Grid[N][N];
int n ,m ,k;

inline bool isValid(int i ,int j) {
    return (i > 0 && j > 0 && i <= n && j <= m && Grid[i][j] != 0);
}

int BFS( ii Start , ii End ) {
        vector< vector<int> > Dist(n + 1 , vector<int>(m + 1 ,OO) );
        Dist[ Start.F ][ Start.S ] = 0;
        queue< ii > Q; Q.push( Start );

        while( !Q.empty() ) {
                ii front = Q.front(); Q.pop();

                int i = front.F , j = front.S;
                int Color = Grid[i][j];
                for(int x = 0 ; x < (int)kColorIdx[ Color ].size() ; x++) {
                        ii idx = kColorIdx[ Color ][ x ];
                        Dist[ idx.F ][ idx.S ] = Dist[i][j];

                        for(int move = 0 ; move < 4 ; move ++) {
                                int newI = idx.F + dx[ move ];
                                int newJ = idx.S + dy[ move ];

                                if( isValid(newI ,newJ) && Dist[ newI ][ newJ ] == OO && Grid[ newI ][ newJ ] != Color ) {
                                        Dist[ newI ][ newJ ] = Dist[ idx.F ][ idx.S ] + 1;
                                        Q.push( ii(newI ,newJ) );
                                }
                        }
                }
        }

        return Dist[ End.F ][ End.S ];
}

int main()
{
    scanf("%d%d%d" ,&n ,&m ,&k);
    kColorIdx.assign(k + 1 ,vector<ii>());

    ii stIdx = ii(0 ,0) ,edIdx = ii(0 ,0);
    for(int i = 1 ; i <= n ; i++){
        for(int j = 1 ; j <= m ; j++){
            scanf("%d" ,&Grid[i][j]);
            int Color = Grid[i][j];

            kColorIdx[ Color ].push_back( ii(i ,j) );

            if( Color == 1 ) stIdx = ii(i ,j);
            if( Color == k ) edIdx = ii(i ,j);
        }
    }

    printf( "%d" ,BFS(stIdx ,edIdx) );
    return 0;
}