组合数学
View Code #include < iostream > #include < cstdio > #include < cstdlib > #include < cstring > using namespace std; char st[ 15 ]; int com( int n, int r){ if (n - r < r) r = n - r; int i, j, s = 1 ; for (i = 0 , j = 1 ; i < r; ++ i) { s *= (n - i); for (; j <= r && s % j == 0 ; ++ j) s /= j; } return s;} int main(){ // freopen("t.txt", "r", stdin); gets(st); int len = strlen(st); if (len == 1 ) { printf( " %d\n " , st[ 0 ] - ' a ' + 1 ); return 0 ; } bool ok = true ; if (st[ 0 ] <= ' z ' && st[ 0 ] >= ' a ' ) ok = true ; else ok = false ; for ( int i = 1 ; i < len; i ++ ) if ( ! (st[i] <= ' z ' && st[i] >= ' a ' && st[i] > st[i - 1 ])) ok = false ; if ( ! ok) { printf( " 0\n " ); return 0 ; } int ans = 26 ; for ( int i = 2 ; i < len; i ++ ) ans += com( 26 , i); ans += com( 26 , len) - com( 26 - (st[ 0 ] - ' a ' ), len); for ( int i = 1 ; i < len; i ++ ) ans += com( 26 - (st[i - 1 ] - ' a ' + 1 ), len - i) - com( 26 - (st[i] - ' a ' ), len - i); printf( " %d\n " , ans + 1 ); return 0 ;}