week15- D. Construct a Walking Path!, Author Solution

#include<bits/stdc++.h>
const int SIZE = 200 * 1000 + 1;
int N,c[SIZE];
int change(){
    for(int i=1;i<N-1;i++){
        if(c[i+1]<=0){
            for(int j=i;j<=N;j++){
                if((i-j)%2==0)c[j]--;
                else c[j]++;
            }
            return i;
        }
    }
    if(c[N]<0){
        c[N-1]--;
        c[N]++;
        return N-1;
    }
    if(c[N]>0){
        c[N]--;
        return N;
    }
    return -1;
}
int main(){
    scanf("%d",&N);
    for(int i=1;i<=N;i++){
        scanf("%d",&c[i]);
        c[i]=c[i]*2-c[i-1];
    }
    int s=change();
    int t=change();
    int z=change();
    if(z!=-1)return 0*puts("Impossible");
    if(s==-1){s=N-1,t=N;c[N-1]--;}
    printf("%d\n",s);
    while(s!=1){
        s--;
        c[s]--;
        printf("<");
    }
    while(s<t){
        printf(">");
        c[s]--;
        while(c[s]>0){
            printf("<>");
            c[s]-=2;
        }
        s++;
    }
    while(s<N){
        c[s]--;
        printf(">");
        s++;
    }
    while(s>t){
        s--;
        if(!c[s])break;
        printf("<");
        c[s]--;
        while(c[s]>0){
            printf("><");
            c[s]-=2;
        }
    }
}