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POJ - 3669 Meteor Shower(bfs)

2024-09-09 07:13:47   216人阅读

题意：某人在时刻0从原点出发，在第一象限范围内移动。已知每个炸弹爆炸的地点和时刻，炸弹爆炸可毁坏该点和它上下左右的点。不能经过已毁坏的点，也不能在某点毁坏的时候位于该点。不会被炸弹毁坏的地方是安全之处，问某人到达安全之处的最短时间。

分析：bfs即可。注意：1、某点多次爆炸或受爆炸点影响而毁坏，取最早时间为该点的毁坏时间。2、bfs走过的点不能再走，注意标记。

#pragma comment(linker, "/STACK:102400000, 102400000")#include<cstdio>#include<cstring>#include<cstdlib>#include<cctype>#include<cmath>#include<iostream>#include<sstream>#include<iterator>#include<algorithm>#include<string>#include<vector>#include<set>#include<map>#include<stack>#include<deque>#include<queue>#include<list>#define Min(a, b) ((a < b) ? a : b)#define Max(a, b) ((a < b) ? b : a)const double eps = 1e-8;inline int dcmp(double a, double b){    if(fabs(a - b) < eps) return 0;    return a > b ? 1 : -1;}typedef long long LL;typedef unsigned long long ULL;const int INT_INF = 0x3f3f3f3f;const int INT_M_INF = 0x7f7f7f7f;const LL LL_INF = 0x3f3f3f3f3f3f3f3f;const LL LL_M_INF = 0x7f7f7f7f7f7f7f7f;const int dr[] = {0, -1, 0, 1, -1, -1, 1, 1};const int dc[] = {-1, 0, 1, 0, -1, 1, -1, 1};const int MOD = 1e9 + 7;const double pi = acos(-1.0);const int MAXN = 300 + 10;const int MAXT = 10000 + 10;using namespace std;int vis[MAXN][MAXN];int a[MAXN][MAXN];bool judge(int x, int y){    return x >= 0 && y >= 0;}int bfs(int sx, int sy){    queue<int> x, y, step;    x.push(sx);    y.push(sy);    step.push(0);    a[sx][sy] = 1;    while(!x.empty()){        int tmpx = x.front();        x.pop();        int tmpy = y.front();        y.pop();        int tmpstep = step.front();        step.pop();        if(vis[tmpx][tmpy] == INT_INF) return tmpstep;        for(int i = 0; i < 4; ++i){            int tx = tmpx + dr[i];            int ty = tmpy + dc[i];            if(judge(tx, ty)){                if(vis[tx][ty] == INT_INF) return tmpstep + 1;                if(a[tx][ty]) continue;                if(vis[tx][ty] > tmpstep + 1){                    x.push(tx);                    y.push(ty);                    step.push(tmpstep + 1);                    a[tx][ty] = 1;                }            }        }    }    return -1;}int main(){    int M;    scanf("%d", &M);    memset(vis, INT_INF, sizeof vis);    while(M--){        int x, y, t;        scanf("%d%d%d", &x, &y, &t);        vis[x][y] = Min(vis[x][y], t);        for(int i = 0; i < 4; ++i){            int tmpx = x + dr[i];            int tmpy = y + dc[i];            if(judge(tmpx, tmpy)) vis[tmpx][tmpy] = Min(vis[tmpx][tmpy], t);        }    }    int ans = bfs(0, 0);    printf("%d\n", ans);    return 0;}

　　

POJ - 3669 Meteor Shower(bfs)


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