查看原题'" class='mdui-btn mdui-btn-raised'>点击加载点击跳转其实下面给出的$a$数组没什么鸟用列出方程：$E = \sum_{i=0}^{n-1} \frac 1n \times ( i+ flag \times E)$解方程：$$E = \sum{i=0}^{n-1} \frac 1n \times ( i+ flag \times E)\\E = \sum{i=0}^{n-1} \frac in + (1 - \frac mn)E \\\frac mnE = \frac {\frac 12n(n-1)}n\\E = \frac {n(n-1)}{2m}$……