``` ans+=sqrt((arr[n][0]-arr[n+1][0])*(arr[n][0]-arr[n+1][0])+(arr[n][1]-arr[n+1][1])*(arr[n][1]-arr[n+1][1])); ``` $n$ 改成 $i$ by yuheng_wang080904 @ 2022-12-10 13:51:51