我觉得是最长解了。。。勿抄

#include<stdio.h>
int main(){
    int n;
    scanf("%d",&n);
    int a[n+1];
    for(int i=0;i<=n;i++){
        scanf("%d ",&a[i]);
    }
    for(int m=n,i=0;m>=0,i<=n;m--,i++){
        if(a[i]!=0){
            if(m!=n){
                if(m==0){
                    if(a[i]>0){
                        printf("+%d",a[i]);
                    }else{
                        printf("%d",a[i]);                    
                    }
                }else if(m==1){
                    if(a[i]==1){
                        printf("+x");
                    }else if(a[i]==-1){
                    printf("-x");
                    }else{
                        if(a[i]>0){
                            printf("+%dx",a[i]);
                        }else{
                            printf("%dx",a[i]);                    
                        }
                    }
                }else{
                    if(a[i]==1){
                        printf("+x^%d",m);
                    }else if(a[i]==-1){
                        printf("-x^%d",m);
                    }else{
                        if(a[i]>0){
                            printf("+%dx^%d",a[i],m);
                        }else{
                            printf("%dx^%d",a[i],m);                    
                        }
                    }
                }
            }else{
                if(m==0){
                    if(a[i]>0){
                        printf("%d",a[i]);
                    }else{
                        printf("%d",a[i]);                    
                    }
                }else if(m==1){
                    if(a[i]==1){
                        printf("x");
                    }else if(a[i]==-1){
                        printf("-x");
                    }else{
                        if(a[i]>0){
                            printf("%dx",a[i]);
                        }else{
                            printf("%dx",a[i]);                    
                        }
                    }
                }else{
                    if(a[i]==1){
                        printf("x^%d",m);
                    }else if(a[i]==-1){
                        printf("-x^%d",m);
                    }else{
                        if(a[i]>0){
                            printf("%dx^%d",a[i],m);
                        }else{
                            printf("%dx^%d",a[i],m);                    
                        }
                    }
                }
            }
        }
    }
    return 0;
}