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终于到70了！！！！原来此题是哈希，一开始没看出来。 发现一条性质：如果一段区间是平衡的，那么这段区间的所有数xor一下结果是0 或 2^k-1，这样就可以预处理出s[i],表示a[0] xor a[1] xor a[2] xor ... xor a[i]。要看[x,y]是否平衡，只需看s[y] xor s[x-1]是否等于0或2^k-1就行了。 Followed by:
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