标签:style blog class c code java
堡垒问题是在学习递归回溯时的一个经典问题,在递归求解此类问题时,总是先判断当前状态是否行,如果可行,则试着放置一个问题的解,继续递归搜索。递归结束后之后要将状态改变回来,因为前提只是假设先放置着问题的解,之后肯定要修改回来才能保证问题解的正确性。如果忘记修改状态回来,程序肯定会出错。在搜索时,注意条件可以进行剪枝,避免不必要的递归,节约时间。最重要的是要明确递归结束条件。
/* * @author Panoss */ #include<iostream> #include<cstdio> #include<cstring> #include<string> #include<algorithm> #include<vector> #include<ctime> #include<stack> #include<queue> #include<list> using namespace std; #define DBG 1 #define fori(i,a,b) for(int i = (a); i < (b); i++) #define forie(i,a,b) for(int i = (a); i <= (b); i++) #define ford(i,a,b) for(int i = (a); i > (b); i--) #define forde(i,a,b) for(int i = (a); i >= (b); i--) #define forls(i,a,b,n) for(int i = (a); i != (b); i = n[i]) #define mset(a,v) memset(a, v, sizeof(a)) #define mcpy(a,b) memcpy(a, b, sizeof(a)) #define dout DBG && cerr << __LINE__ << " >>| " #define checkv(x) dout << #x"=" << (x) << " | "<<endl #define checka(array,a,b) if(DBG) { \ dout<<#array"[] | " << endl; forie(i,a,b) cerr <<"["<<i<<"]="<<array[i]<<" |"<<((i-(a)+1)%5?" ":"\n"); if(((b)-(a)+1)%5) cerr<<endl; } #define redata(T, x) T x; cin >> x #define MIN_LD -2147483648 #define MAX_LD 2147483647 #define MIN_LLD -9223372036854775808 #define MAX_LLD 9223372036854775807 #define MAX_INF 18446744073709551615 inline int reint() { int d; scanf("%d",&d); return d; } inline long relong() { long l; scanf("%ld",&l); return l; } inline char rechar() { scanf(" "); return getchar(); } inline double redouble() { double d; scanf("%lf", &d); return d; } inline string restring() { string s; cin>>s; return s; } int n,ans; char a[4][4]; bool IsCanPlace(int x, int y) { forde(i,x-1,0) { if(a[i][y]==‘0‘) return false; if(a[i][y]==‘X‘) break; } forde(i,y-1,0) { if(a[x][i]==‘0‘) return false; if(a[x][i]==‘X‘) break; } return true; } void DFS(int k, int current_ans) { if(k==n*n) { ans = max(ans,current_ans); return ; } else { int x = k/n; int y = k%n; if(a[x][y]==‘.‘&&IsCanPlace(x,y)) { a[x][y] =‘0‘; ///先放一个堡垒 DFS(k+1,current_ans+1); a[x][y] =‘.‘; ///搜索结束后再放置回来 } DFS(k+1,current_ans);///搜索不放的状态 } } int main() { while(scanf("%d",&n)==1&&n) { fori(i,0,n) scanf("%s",a[i]); ans=0; DFS(0,0); cout<<ans<<endl; } return 0; }
标签:style blog class c code java
原文地址:http://www.cnblogs.com/Panoss/p/3740088.html