Hdu2717 & hdu1548-retrain BFS

Hdu2717

In the question, N belongs to [1-100000] and cannot go out of 100000. At the beginning, n can always be written in half. This error is reported twice.

In addition, the question is to find the minimum number of steps, or BFs. This question is purely an exercise.

Question:

Start Point and end point. You can take one step forward and one step backward. <1. Calculate the minimum number of steps.

Analysis:

BFS.

Code:

# Include <stdio. h> # include <queue> # include <string. h> bool N [100002]; // indicates whether int min, K; struct info {int A; int C ;}; STD: queue <info> q; bool operator <(Info X, info y) {return X. c> Y. c;} void BFS (Info X) {info Y, Z, W; q. push (x); While (! Q. empty () {x = Q. front (); q. pop (); N [X. a] = 1; if (X. A = k) {min = x. c; break;} y. A = 2 * X. a; Y. C = x. c + 1; Z. A = x. A + 1; Z. C = x. c + 1; W. A = x. a-1; W. C = x. c + 1; if (Y. a> 0 & Y. A <= 100000 & N [Y. a] = 0) Q. push (y); If (Z. a> 0 & Z. A <= 100000 & N [Z. a] = 0) Q. push (z); If (W. a> 0 & W. A <= 100000 & N [W. a] = 0) Q. push (w) ;}while (! Q. Empty () {q. Pop () ;}} int main () {int N; while (~ Scanf ("% d", & N, & K) {memset (n, 0, sizeof (n); N [N] = 1; min = k-N; Info X; X. A = N; X. C = 0; If (n> = k) min = n-k; else BFS (x); printf ("% d \ n", min);} return 0 ;}

Hdu1548

Still BFs. When it cannot be reached, output-1;

You can use priority queue optimization.

#include<stdio.h>#include<queue>#include<string.h>bool N[202];int num[202];int e,n;struct info{int a;int c;};std::priority_queue<info> Q;bool operator<(info x,info y){return x.c>y.c;}int BFS(info x){info y,z,w;Q.push(x);while(!Q.empty()){x=Q.top();Q.pop();N[x.a]=1;if(x.a==e) {while(!Q.empty())Q.pop();return x.c;}y.a=x.a+num[x.a];y.c=x.c+1;z.a=x.a-num[x.a];z.c=x.c+1;if(y.a>0&&y.a<=n&&N[y.a]==0)  Q.push(y);if(z.a>0&&z.a<=n&&N[z.a]==0)  Q.push(z);}return -1;}int main() {int b,i;while(scanf("%d",&n)&&n!=0){scanf("%d%d",&b,&e);memset(N,0,sizeof(N));for(i=0;i<n;i++)scanf("%d",&num[i+1]);info x;x.a=b;x.c=0;printf("%d\n",BFS(x));}return 0;}