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DFS 从左往右搜+减枝

注意数组越界问题！！！

#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;const int N = 30 ;int col [N] ;int vis [N] ;char a [3][N] ;int n;int id ( char ch ) {    return ch - 'A' + 1;}void dfs ( int li , int ro , int tmp ) {    if ( li == 0 ) {        if ( tmp != 0 ) return ;        for ( int i = 1 ; i <= n ; ++ i )             printf ( "%d " , col [i] );        exit(0);    }    for ( int i = li - 1 ; i >= 1 ; -- i ){        int w1 = col [ id ( a [0] [i]  ) ] ;        int w2 = col [ id ( a [1] [i]  ) ] ;        int w3 = col [ id ( a [2] [i]  ) ] ;        if ( w1 == -1 || w2 == -1 || w3 == -1 ) continue ;        if ( (w1 + w2)%n != w3 && ( w1 + w2 + 1 )%n != w3 ) return ;    }    if ( col [ id ( a [ro] [li]  ) ] == -1 ) {        if ( ro != 2 ) {            for ( int i = n-1 ; i >= 0 ; -- i ) if ( ! vis [i] ) {                col [ id ( a [ro] [li] ) ] = i ;                vis [i] = 1;                dfs ( li , ro + 1 , tmp ) ;                col [ id ( a [ro] [li] ) ] = -1 ;                vis [i] = 0;            }        }else {            int x = col [id(a[0][li])] + col [id(a[1][li])] + tmp ;            if ( vis [x%n] != 0 ) return ;            vis [x%n] = 1 ;            col [ id( a [2] [li] ) ] = x%n ;            dfs ( li-1 , 0 , x/n );            col [ id( a [2] [li] ) ] = -1 ;            vis [x%n] = 0 ;        }    }else {        if ( ro != 2 )             dfs ( li , ro+1 , tmp );        else {            int x = col [id(a[0][li])] + col [id(a[1][li])] + tmp ;            if ( col [ id( a [2] [li] ) ] != x % n ) return ;            dfs ( li-1 , 0 , x / n );        }    }}int main () {    memset ( vis , 0 , sizeof vis );    memset ( col , -1 , sizeof col );    scanf ( "%d" , &n ) ;getchar();    for ( int i = 0 ; i < 3 ; ++ i )                scanf ( "%s" , a [i] + 1 ) ;    dfs ( n , 0 , 0 ) ;    return 0 ;}
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