仅观察杨辉三角元素的奇偶性,将杨辉三角变换为:
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1 |
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1 | 1 | 1 |
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1 | 0 | 1 | 0 | 1 |
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1 | 1 | 0 | 1 | 0 | 1 | 1 |
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1 | 0 | 0 | 0 | 1 | 0 | 0 | 0 | 1 |
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1 | 1 | 1 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | 1 |
1
111
101
110
100
111(0)
...
注意第六行111后是0,所以可以特殊处理前两行输出为“-1”,后续可根据行数n按照(n-2)%4来得出case依次为2,3,2,4。