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#include <bits/stdc++.h>
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using namespace std;
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const int INF = 0x3f3f3f3f;
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int main() {
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/**
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数学表示：
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a ^ a ^ b = b;
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a ^ b ^ a = b;
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b ^ a ^ a = b;
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原理：
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可用穷举法证明：
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异或运算：1 ^ 1 = 0；1 ^ 0 = 1; 0 ^ 1 = 1; 0 ^ 0 = 0;
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穷举： 1 ^ 1 ^ 1 = 1；
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1 ^ 1 ^ 0 = 0；
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1 ^ 0 ^ 1 = 0；
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0 ^ 1 ^ 1 = 0；
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1 ^ 0 ^ 0 = 1；
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0 ^ 1 ^ 0 = 1；
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0 ^ 0 ^ 1 = 1；
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0 ^ 0 ^ 0 = 0；
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可知任意1或0出现两次，即可抵消。 从而推广至多个位（bit）。
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一个数异或同一个数两次,结果还是那个数。 且异或的顺序可变。
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证明：https://www.zhihu.com/question/62003033
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*/
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return 0;
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}
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