tmp heapsort

other/heapsort_test.go

@@ -0,0 +1,58 @@
+// Problem:
+// Implement heapsort.
+//
+// Mechanic:
+// Similar to selection sort, repeatedly choose the largest item and move it to
+// the end of the array using a heap.
+//
+// Cost:
+// O(nlogn) time and O(1) space.
+
+package other
+
+import (
+	"testing"
+
+	"github.com/hoanhan101/algo/common"
+)
+
+func TestHeapsort(t *testing.T) {
+	tests := []struct {
+		in       []int
+		expected []int
+	}{
+		{[]int{}, []int{}},
+		{[]int{1}, []int{1}},
+		{[]int{1, 2}, []int{1, 2}},
+		{[]int{2, 1}, []int{1, 2}},
+		{[]int{2, 1, 3}, []int{1, 2, 3}},
+		{[]int{1, 1, 1}, []int{1, 1, 1}},
+		{[]int{2, 1, 2}, []int{1, 2, 2}},
+		{[]int{1, 2, 4, 3, 6, 5}, []int{1, 2, 3, 4, 5, 6}},
+		{[]int{6, 2, 4, 3, 1, 5}, []int{1, 2, 3, 4, 5, 6}},
+		{[]int{6, 5, 4, 3, 2, 1}, []int{1, 2, 3, 4, 5, 6}},
+	}
+
+	for _, tt := range tests {
+		heapsort(tt.in)
+		common.Equal(t, tt.expected, tt.in)
+	}
+}
+
+func heapsort(in []int) {
+	minIndex := 0
+	for i := 0; i < len(in)-1; i++ {
+		minIndex = i
+		// find the minimum in the rest of the array.
+		for j := i + 1; j < len(in); j++ {
+			if in[j] < in[minIndex] {
+				minIndex = j
+			}
+		}
+
+		// swap the minimum value with the first value.
+		tmp := in[i]
+		in[i] = in[minIndex]
+		in[minIndex] = tmp
+	}
+}