hihoCoder 1527 快速乘法

#include<bits/stdc++.h>
using namespace std;

const int N = 1e6+;
char a[N];
int main()
{
    scanf("%s",a+);
    int n = strlen(a+);
    int l = ,r = n;
    while(l <= n && a[l] == '')
        l++;
    while(r >=  && a[r] == '')
        r--;
    int u = ,d = ;
    for(int i = r-;i >= l;i--)
        if(a[i] == '')
            u = min(u,d)+;
        else
            d = min(u,d)+;
    printf("%d\n",u*-);
    return ;
}