skew数——数学递推
https://www.nowcoder.com/pat/2/problem/266
吐槽：找到权值公式x[k] = 2*x[k-1] +1，然后先算出来。
#include<cstdio>
#include<cstring>
int x[50];
int main(){
x[0]=1;
x[1]=3;
for(int i=2;i<32;i++){
x[i] = 2*x[i-1] + 1;
}
char str[100];
while(scanf("%s",str) != EOF){
int len = strlen(str);
int sum = 0;
for(int i = 0; i < len; i++){
sum += (str[i] - '0')*x[len - 1 - i];
}
printf("%d\n",sum);
}
} 