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	`1`	`+### 3681.Maximum-XOR-of-Subsequences`
	`2`	`+`
	`3`	`+这是一道"异或空间线性基"的模版题。`
	`4`	`+`
	`5`	+首先定义"异或空间线性基"。对于一组数字集合nums,任意选取若干进行异或操作所能构成的结果记作空间S。如果另一组数字Basis同样也能构成S,并且Basis所需的数字最少,那么Basis就成为原数字集合的一组"异或空间线性基"。举个例子,比如nums={9,11,12,14},它所能构成的异或空间S={2,5,7,9,11,12,14}. 通过某种算法,我们可以找到一组线性基B={12,5,2},并且可以验证B能构造的异或空间也是S。另外,我们所构造的线性基有一个特点,每个元素的leading one的位置都不相同。比如{12,5,2},其二进制表达就是{1100,0101,0010},可以观察到最高位的位置依次降低。
	`6`	`+`
	`7`	`+假设我们能找到nums的一组线性基B,那么nums能组成的最大异或值,等价于其线性基B能组成的最大异或值。而对于B,由于有前述的性质(最高位的位置依次降低),我们可以用贪心法来从大到小进行选择:第i个元素的选择取决于答案的第i个bit位是否会退化。`
	`8`	+```cpp
	`9`	`+int ret = 0;`
	`10`	`+for (int b: basis) {`
	`11`	`+ ret = max(ret, ret^b);`
	`12`	`+}`
	`13`	+```
	`14`	`+`
	`15`	`+接下来我们学习如何构造这样的异或空间线性基。举个例子:a=2, b=5, c=11, d=6`
	`16`	+```
	`17`	`+ 3 2 1 0`
	`18`	`+a`
	`19`	`+b`
	`20`	`+c`
	`21`	`+d`
	`22`	+```

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