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@@ -0,0 +1,74 @@
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+package main
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+
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+import (
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+ "fmt"
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+ "math/rand"
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+ "time"
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+)
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+
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+type ints []int
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+
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+func (is ints) less(i, j int) bool { return is[i] < is[j] }
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+func (is ints) swap(i, j int) { is[i], is[j] = is[j], is[i] }
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+
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+func (is ints) getN(n int) int { // Get the Nth smallest number.
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+ l := len(is)
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+ lo, hi := 0, l-1
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+ for lo < hi {
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+ m := is.partition(lo, hi)
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+ if m == n-1 {
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+ return is[m]
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+ } else if m < n-1 {
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+ lo = m + 1
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+ } else {
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+ hi = m - 1
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+ }
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+ }
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+ return is[lo]
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+}
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+
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+func (is ints) sort() {
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+ l := len(is)
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+ rand.Shuffle(l, is.swap)
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+ is.qsort(0, l-1)
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+}
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+
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+func (is ints) qsort(lo, hi int) {
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+ if hi <= lo {
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+ return
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+ }
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+ m := is.partition(lo, hi)
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+ is.qsort(lo, m-1)
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+ is.qsort(m+1, hi)
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+}
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+
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+func (is ints) partition(lo, hi int) int {
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+ i, j := lo, hi+1
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+ for {
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+ for i++; is.less(i, lo) && i != hi; i++ {
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+ }
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+ for j--; is.less(lo, j) && j != lo; j-- {
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+ }
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+ if j <= i {
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+ break
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+ }
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+ is.swap(i, j)
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+ }
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+ is.swap(lo, j)
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+ return j
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+}
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+
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+func main() {
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+ var n int
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+ fmt.Scan(&n)
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+ rand.Seed(time.Now().Unix())
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+ var list ints = make([]int, n)
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+ for i := range list {
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+ list[i] = rand.Intn(2 * n)
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+ }
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+ fmt.Println(list)
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+ m := list.getN(n / 2)
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+ list.sort()
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+ fmt.Println(list)
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+ fmt.Println(m, list[n/2-1])
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+}
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