|洛谷|NOIP2004|搜索|P1092 虫食算

https://www.luogu.org/problem/show?pid=1092

这道搜索折腾我好久。。结果还是TLE一个点。。

从后往前搜索，从上往下搜索

很多剪枝不一一说了看代码吧

90分代码

#include
#include
#include
#include
#define ms(i,j) memset(i,j, sizeof i);
using namespace std;
int n; 
int A[30], B[30], C[30];
int h[30];
bool vi[30];
int dfs(int nowc, int nows, int ys, int a)
{        
    if (a==n+1) 
    {
        //查看下面的算式是否合法，这里很重要，填完了数不代表前面的成立 
        if (nowc!=1)
        {
            int u = nowc; int YS = ys;
            while (u>0)
            {
                if ((h[A[u]]+h[B[u]]+YS)%n!=h[C[u]]) return 0;
                YS = (h[A[u]]+h[B[u]]+YS)/n;
                u--;
            }
        }
        for (int i=0;i=0&&h[B[nowc]]>=0)
                                if ((i+h[B[nowc]]+ys)%n!=h[C[nowc]]) continue;
                                h[A[nowc]] = i;
                                vi[i] = true; 
                                dfs(nowc, nows+1, ys, a+1);//DFSSSSSS 
                                h[A[nowc]] = -1;
                                vi[i] = false;
                            }
                        }
                    } else dfs(nowc, nows+1, ys, a);//DFSSSSSS 
                    break;
                }
                case 2 :
                {
                    if (h[B[nowc]]<0) 
                    { 
                        for (register int i=0;i=0&&h[A[nowc]]>=0)
                                if ((i+h[A[nowc]]+ys)%n!=h[C[nowc]]) continue;
                                h[B[nowc]] = i;
                                vi[i] = true;
                                dfs(nowc, nows+1, ys, a+1);//DFSSSSSS 
                                h[B[nowc]] = -1;
                                vi[i] = false;
                            }
                        } 
                    }else dfs(nowc, nows+1, ys, a);//DFSSSSSS 
                    break;
                }
                case 3 :
                {
                    if (h[C[nowc]]<0)
                    {
                        if (h[A[nowc]]<0||h[B[nowc]]<0) return 0;
                        if (!vi[(h[A[nowc]]+h[B[nowc]]+ys)%n])
                        {
                            vi[(h[A[nowc]]+h[B[nowc]]+ys)%n] = true;
                            h[C[nowc]] = (h[A[nowc]]+h[B[nowc]]+ys)%n;
                            dfs(nowc-1, 1, (h[A[nowc]]+h[B[nowc]]+ys)/n, a+1);//DFSSSSSS 
                            h[C[nowc]] = -1;
                            vi[(h[A[nowc]]+h[B[nowc]]+ys)%n] = false;
                        } else return 0;
                    } else 
                    {
                        if ((h[A[nowc]]+h[B[nowc]]+ys)%n!=h[C[nowc]]) return 0;
                        dfs(nowc-1, 1, (h[A[nowc]]+h[B[nowc]]+ys)/n, a);//DFSSSSSS 
                    }
                    break;
                }
        }
    }
}
int main()
{
    scanf("%d\n", &n);
    for (int i=1;i<=n;i++) {char ch = getchar(); A[i] = ch-'A';}
    scanf("\n");
    for (int i=1;i<=n;i++) {char ch = getchar(); B[i] = ch-'A';}
    scanf("\n");
    for (int i=1;i<=n;i++) {char ch = getchar(); C[i] = ch-'A';}
    ms(h, -1); ms(vi, false);
    dfs(n,1,0,1);
    return 0;
}