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UVA 10564 Paths through the Hourglass[DP 打印]

 

UVA - 10564
Paths through the Hourglass

 

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题意:

要求从第一层走到最下面一层,只能往左下或右下走
问有多少条路径之和刚好等于S? 如果有的话,输出字典序最小的路径。

f[i][j][k]从下往上到第i层第j个和为k的方案数
上下转移不一样,分开处理
没必要判断走出沙漏
打印方案倒着找下去行了,尽量往左走
 
沙茶的忘注释掉文件WA好多次
 
#include <iostream>#include <cstdio>#include <algorithm>#include <cstring>using namespace std;const int N=25,M=505,INF=1e9;typedef long long ll;inline int read(){    char c=getchar();int x=0,f=1;    while(c<0||c>9){if(c==-)f=-1;c=getchar();}    while(c>=0&&c<=9){x=x*10+c-0;c=getchar();}    return x*f;}int n,s,w[N<<1][N];ll f[N<<1][N][M];void dp(){    memset(f,0,sizeof(f));    for(int j=1;j<=n;j++)        f[n+n-1][j][w[n+n-1][j]]=1;        //xia    for(int i=n+n-2;i>=n;i--)        for(int j=1;j<=i-n+1;j++)            for(int k=w[i][j];k<=s;k++)                f[i][j][k]=f[i+1][j][k-w[i][j]]+f[i+1][j+1][k-w[i][j]];    //shang    for(int i=n-1;i>=1;i--)        for(int j=1;j<=n-i+1;j++)            for(int k=w[i][j];k<=s;k++)                f[i][j][k]=f[i+1][j][k-w[i][j]]+f[i+1][j-1][k-w[i][j]];    }void print(int i,int j,ll k){//printf("print %d %d %d\n",i,j,k);    if(i==n+n-1) return;    if(i<n){        if(j>1&&f[i+1][j-1][k-w[i][j]]){            putchar(L);            print(i+1,j-1,k-w[i][j]);        }else{            putchar(R);            print(i+1,j,k-w[i][j]);        }    }else{        if(f[i+1][j][k-w[i][j]]){            putchar(L);            print(i+1,j,k-w[i][j]);        }else{            putchar(R);            print(i+1,j+1,k-w[i][j]);        }    }}int main(){    //freopen("1.in","r",stdin);    //freopen("1.out","w",stdout);    while(scanf("%d%d",&n,&s)!=EOF&&(n||s)){        memset(w,0,sizeof(w));        for(int i=1;i<=n;i++)            for(int j=1;j<=n-i+1;j++) w[i][j]=read();        for(int i=n+1;i<=n+n-1;i++)            for(int j=1;j<=i-n+1;j++) w[i][j]=read();        dp();        int p=0;        ll sum=0;        for(int i=n;i>=1;i--) if(f[1][i][s]){p=i;sum+=f[1][i][s];}                printf("%lld\n",sum);        if(p) printf("%d ",p-1),print(1,p,s);        putchar(\n);    }}

 

UVA 10564 Paths through the Hourglass[DP 打印]