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递推公式及推导过程。

Posted by denghongchao at 2009-08-14 18:43:58 on Problem 2663
先假设没2竖为1 单位。
对当前解a[i] ,有
1.在此处放一单位的积木。等于a[i-1]*3;
2.与前面相连接。连接的方案有 2 * (a[i-2] + a[i-3] +......+a[0]);
a[i] = 3*a[i-1] + 2*(a[i-2] + a[i-3] +......+a[0]);
a[i-1] = 3*a[i-2] + 2*(a[i-3] + a[i-3] +......+a[0]);
a[i-1] - a[i-2] = 2*(a[i-2] + a[i-3] +......+a[0]);

解得a[i] = a[i-1] * 4 - a[i-2];
至于为何要a[0] = 1,从公式中就可看到因为要一直取到最前面一个单位。这时也有2种情况。故a[0] = 1 能从理论上运算。。。。这是我的理解,见笑了。

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