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// @Title: 二倍数对数组 (Array of Doubled Pairs)
// @Author: 15816537946@163.com
// @Date: 2022-04-01 22:45:08
// @Runtime: 64 ms
// @Memory: 9.4 MB
func canReorderDoubled(arr []int) bool {
    cnt := make(map[int]int, len(arr))
    for _, x := range arr {
        cnt[x]++
    }
    if cnt[0]%2 == 1 {
        return false
    }

    vals := make([]int, 0, len(cnt))
    for x := range cnt {
        vals = append(vals, x)
    }
    sort.Slice(vals, func(i, j int) bool { return abs(vals[i]) < abs(vals[j]) })

    for _, x := range vals {
        if cnt[2*x] < cnt[x] { // 无法找到足够的 2x 与 x 配对
            return false
        }
        cnt[2*x] -= cnt[x]
    }
    return true
}

func abs(x int) int {
    if x < 0 {
        return -x
    }
    return x
}