{"trustable":false,"sections":[{"title":"","value":{"format":"MD","content":"给n个整数,定义一个数是有序的当且仅当它左边的数都小于等于它,它右边的数都大于等于它,排列这n个整数能组成多少个序列使得所有数都是无序的"}},{"title":"input","value":{"format":"MD","content":"第一行一个整数 n (1 ≤ n ≤ 5000)\n第二行n个整数a[i], 0 ≤ ai ≤ 10^9"}},{"title":"output","value":{"format":"MD","content":"答案对1e9+9取余"}},{"title":"","value":{"format":"MD","content":"输入\n4\n0 1 2 3\n输出\n14\n解释: \n为\n1 0 3 2\n1 2 3 0\n1 3 0 2\n1 3 2 0\n2 0 3 1\n2 1 3 0\n2 3 0 1\n2 3 1 0\n3 0 1 2\n3 0 2 1\n3 1 0 2\n3 1 2 0\n3 2 0 1\n3 2 1 0\n输入\n5\n1 1 2 1 1\n\n输出\n1\n输入\n13\n1 2 3 4 5 6 7 8 9 10 11 12 13\n输出\n298600727"}}]}