我们称一个数字序列 $x(1), x(2), \dots, x(k)$ 为 zigzag 序列，如果其中任意三个连续元素都不构成非递增或非递减序列。更准确地说，对于所有 $i = 1, 2, \dots, k-2$，必须满足 $x(i+1) < x(i)$ 且 $x(i+1) < x(i+2)$，或者 $x(i+1) > x(i)$ 且 $x(i+1) > x(i+2)$。
给定两个数字序列 $a(1), a(2), \dots, a(n)$ 和 $b(1), b(2), \dots, b(m)$。本题要求计算它们的最长公共 zigzag 子序列的长度。换句话说，你需要从两个序列中删除若干元素，使得剩余部分相等，且剩余的序列是一个 zigzag 序列。
5 1 2 5 4 3 5 4 1 2 5 3
3
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