1 files changed, 57 insertions, 0 deletions
diff --git a/vendor/github.com/hongshibao/go-algo/selection.go b/vendor/github.com/hongshibao/go-algo/selection.go
new file mode 100644
index 0000000..b17fe70
--- /dev/null
+++ b/vendor/github.com/hongshibao/go-algo/selection.go
@@ -0,0 +1,57 @@
+package algo
+
+import (
+	"math/rand"
+	"sort"
+
+	"github.com/dropbox/godropbox/errors"
+)
+
+// [left, right]
+func Partition(array sort.Interface, left int, right int,
+	pivotIndex int) (int, error) {
+	if pivotIndex < left || pivotIndex > right {
+		return -1, errors.New("Pivot index out of range")
+	}
+	if left < 0 || right >= array.Len() {
+		return -1, errors.New("Array index out of range")
+	}
+	lastIndex := right
+	array.Swap(pivotIndex, lastIndex)
+	leftIndex := left
+	for i := left; i < lastIndex; i++ {
+		if array.Less(i, lastIndex) {
+			array.Swap(leftIndex, i)
+			leftIndex++
+		}
+	}
+	array.Swap(leftIndex, lastIndex)
+	return leftIndex, nil
+}
+
+// k is started from 1
+func QuickSelect(array sort.Interface, k int) error {
+	if k <= 0 || k > array.Len() {
+		return errors.New("Parameter k is invalid")
+	}
+	k--
+	left := 0
+	right := array.Len() - 1
+	for {
+		if left == right {
+			return nil
+		}
+		pivotIndex := left + rand.Intn(right-left+1)
+		pivotIndex, err := Partition(array, left, right, pivotIndex)
+		if err != nil {
+			return errors.Wrap(err, "Partition returns error")
+		}
+		if k == pivotIndex {
+			return nil
+		} else if k < pivotIndex {
+			right = pivotIndex - 1
+		} else {
+			left = pivotIndex + 1
+		}
+	}
+}