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C
D
E(注意一下一条链的话，树根不一定就是1了)
F 辣鸡模拟题，写吐了。
G 很常见的一种思路，先构造出最小的，每次变得最大的就是第i个和第n-i+1个交换，如果发现大了的话，显然可以在剩下的找到和多出来的相等的。