Basic Search entry (2)

Hdu_1548 a strange lift

Question. BFS + priority queue. The minimum number of operations from one location to another.

Code List:

#include<queue>#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>using namespace std;struct edge{    int x;    int t;    friend bool operator<(edge a,edge b){        return a.t>b.t;    }};int N,A,B;int n[205];int vis[205];void bfs(){    priority_queue<edge>q;    edge p,w;    while(q.size()) q.pop();    p.x=A; p.t=0;    q.push(p);    memset(vis,0x5f,sizeof(vis));    vis[A]=0;    int first=1;    while(q.size())    {        p=q.top(); q.pop();        if(p.x==B){            first=0;            printf("%d\n",p.t);            break;        }        w.x=p.x+n[p.x];        w.t=p.t+1;        if(w.x>=1&&w.x<=N&&w.t<vis[w.x])        {            vis[w.x]=w.t;            q.push(w);        }        w.x=p.x-n[p.x];        if(w.x>=1&&w.x<=N&&w.t<vis[w.x])        {            vis[w.x]=w.t;            q.push(w);        }    }    if(first) printf("-1\n");}int main(){    while(scanf("%d",&N)!=EOF)    {        if(N==0) break;        scanf("%d%d",&A,&B);        for(int i=1;i<=N;i++)            scanf("%d",&n[i]);        bfs();    }return 0;}

Hdu_1728 escaping from the maze

BFS does not need to use a priority queue because the question is only about whether the queue can be reached. The number of turns must be smaller than the current number of turns.

Code List:

#include<queue>#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>using namespace std;struct edge{    int x,y;    int pos,turn;};int T,m,n;int k,x1,y1,x2,y2;char s[105][105];int vis[105][105];int xy[4][2]={{0,-1},{-1,0},{0,1},{1,0}};bool bfs(){    if(x1==x2&&y1==y2) return true;    queue<edge>q;    while(q.size()) q.pop();    edge p,w;    memset(vis,0x5f,sizeof(vis));    vis[y1][x1]=-1;    for(int i=0;i<4;i++){        p.x=y1+xy[i][0];        p.y=x1+xy[i][1];        p.pos=i;        p.turn=0;        if(p.x>=0&&p.x<m&&p.y>=0&&p.y<n&&s[p.x][p.y]!='*')        {            vis[p.x][p.y]=0;             q.push(p);        }    }    while(q.size()){        p=q.front(); q.pop();        if(p.x==y2&&p.y==x2) return true;        for(int i=0;i<4;i++){            w.x=p.x+xy[i][0];            w.y=p.y+xy[i][1];            w.pos=i;            if(w.pos!=p.pos) w.turn=p.turn+1;            else             w.turn=p.turn;            if(w.x>=0&&w.x<m&&w.y>=0&&w.y<n&&s[w.x][w.y]!='*'&&w.turn<=vis[w.x][w.y]&&w.turn<=k){                vis[w.x][w.y]=w.turn;                q.push(w);            }        }    }    return false;}int main(){    scanf("%d",&T);    while(T--){        scanf("%d%d",&m,&n);        for(int i=0;i<m;i++)            scanf("%s",s[i]);        scanf("%d%d%d%d%d",&k,&x1,&y1,&x2,&y2);        x1-=1; y1-=1; x2-=1; y2-=1;        if(bfs()) printf("yes\n");        else      printf("no\n");    }return 0;}

Hdu_1180 weird stairway

BFS + priority queue. Note that when the stairs arrive, the status of the stairs can be determined by the current time + current orientation.

Code List:

# Include <queue> # include <cstdio> # include <cstring> # include <iostream> # include <algorithm> using namespace STD; struct edge {int X, Y; int time; friend bool operator <(edge a, edge B) {return. time> B. time ;}}; int M, N; int Sx, Sy; int ex, ey; int vis [25] [25]; char s [25] [25]; int XY [4] [2] = {0,-1}, {-}, {}, {}; void BFS () {priority_queue <edge> q; while (Q. size () Q. pop (); edge P, W; memset (VIS, 0x5f, sizeof (VIS); P. X = SX; p. y = sy; p. time = 0; vis [SX] [sy] = 0; q. push (p); While (Q. size () {P = Q. top (); q. pop (); // cout <p. x <"" <p. Y <"" <p. time <Endl; If (P. X = ex & P. y = ey) {printf ("% d \ n", p. time); break;} For (INT I = 0; I <4; I ++) {W. X = P. X + XY [I] [0]; W. y = P. Y + XY [I] [1]; If (s [W. x] [W. y] = '|') {W. X + = xy [I] [0]; W. Y + = xy [I] [1]; if (I = 1 | I = 3) // I indicates the current orientation {If (P. time % 2 = 0) W. time = P. time + 1; else W. time = P. time + 2;} else {If (P. ti Me % 2 = 0) W. time = P. time + 2; else W. time = P. time + 1 ;}} else if (s [W. x] [W. y] = '-') {W. X + = xy [I] [0]; W. Y + = xy [I] [1]; if (I = 0 | I = 2) {If (P. time % 2 = 0) W. time = P. time + 1; else W. time = P. time + 2;} else {If (P. time % 2 = 0) W. time = P. time + 2; else W. time = P. time + 1 ;}} else W. time = P. time + 1; if (W. x> = 0 & W. x <M & W. y> = 0 & W. Y <n & S [W. x] [W. y]! = '*' & W. time <vis [W. x] [W. y]) {vis [W. x] [W. y] = W. time; q. push (w) ;}}} int main () {While (scanf ("% d", & M, & N )! = EOF) {for (INT I = 0; I <m; I ++) {scanf ("% s", s [I]); For (Int J = 0; j <n; j ++) {If (s [I] [J] = 's') {SX = I; Sy = J ;} if (s [I] [J] = 'T') {EX = I; ey = J ;}} BFS ();} return 0 ;}

Basic Search entry (2)