From 8e9a447ae625780e7b1aa4166cbac7561d33d2ca Mon Sep 17 00:00:00 2001
From: Julian <jb@futureplay.de>
Date: Fri, 28 Sep 2018 19:50:16 +0200
Subject: [PATCH 1/3] add the graham scan in go

---
 contents/graham_scan/code/golang/graham.go | 54 ++++++++++++++++++++++
 contents/graham_scan/graham_scan.md        |  6 +++
 2 files changed, 60 insertions(+)
 create mode 100644 contents/graham_scan/code/golang/graham.go

diff --git a/contents/graham_scan/code/golang/graham.go b/contents/graham_scan/code/golang/graham.go
new file mode 100644
index 000000000..4b405b8e8
--- /dev/null
+++ b/contents/graham_scan/code/golang/graham.go
@@ -0,0 +1,54 @@
+package main
+
+import (
+	"fmt"
+	"math"
+	"sort"
+)
+
+type point struct {
+	x, y int
+}
+
+func counterClockwise(p1, p2, p3 point) bool {
+	return (p3.y-p1.y)*(p2.x-p1.x) >= (p2.y-p1.y)*(p3.x-p1.x)
+}
+
+func polarAngle(ref, point point) float64 {
+	return math.Atan2(float64(point.y-ref.y), float64(point.x-ref.x))
+}
+
+func grahamScan(points []point) []point {
+	sort.Slice(points, func(a, b int) bool {
+		return points[a].y < points[b].y || (points[a].y == points[b].y && points[a].x < points[b].x)
+	})
+
+	start := points[0]
+	points = points[1:]
+
+	sort.Slice(points, func(a, b int) bool {
+		return polarAngle(start, points[a]) < polarAngle(start, points[b])
+	})
+
+	hull := []point{start, points[0], points[1]}
+	for _, p := range points[2:] {
+		for !counterClockwise(hull[len(hull)-2], hull[len(hull)-1], p) {
+			hull = hull[:len(hull)-1]
+		}
+		hull = append(hull, p)
+	}
+
+	return hull
+}
+
+func main() {
+	points := []point{{-5, 2}, {5, 7}, {-6, -12}, {-14, -14}, {9, 9},
+		{-1, -1}, {-10, 11}, {-6, 15}, {-6, -8}, {15, -9},
+		{7, -7}, {-2, -9}, {6, -5}, {0, 14}, {2, 8}}
+
+	fmt.Println("The points in the hull are:")
+	hull := grahamScan(points)
+	for _, p := range hull {
+		fmt.Println(p)
+	}
+}
diff --git a/contents/graham_scan/graham_scan.md b/contents/graham_scan/graham_scan.md
index be8d82280..18889ce1c 100644
--- a/contents/graham_scan/graham_scan.md
+++ b/contents/graham_scan/graham_scan.md
@@ -22,6 +22,8 @@ We can find whether a rotation is counter-clockwise with trigonometric functions
 [import:36-38, lang:"javascript"](code/javascript/graham-scan.js)
 {% sample lang="py" %}
 [import:4-6, lang:"python"](code/python/grahamScan.py)
+{% sample lang="go" %}
+[import:13-15, lang:"golang"](code/golang/graham.go)
 {% endmethod %}
 
 If the output of this function is 0, the points are collinear.
@@ -46,6 +48,8 @@ In the end, the code should look something like this:
 [import:1-30, lang:"javascript"](code/javascript/graham-scan.js)
 {% sample lang="py" %}
 [import:14-27, lang:"python"](code/python/grahamScan.py)
+{% sample lang="go" %}
+[import:21-42, lang:"golang"](code/golang/graham.go)
 {% endmethod %}
 
 ### Bibliography
@@ -65,6 +69,8 @@ In the end, the code should look something like this:
 [import, lang:"javascript"](code/javascript/graham-scan.js)
 {% sample lang="py" %}
 [import, lang:"python"](code/python/grahamScan.py)
+{% sample lang="go" %}
+[import, lang:"golang"](code/golang/graham.go)
 {% endmethod %}
 
 <script>

From dfa182fe46c848716db9759d4c52ef9f89c0eec1 Mon Sep 17 00:00:00 2001
From: Julian <jb@futureplay.de>
Date: Tue, 9 Oct 2018 18:34:40 +0200
Subject: [PATCH 2/3] change the name golang to go

---
 contents/graham_scan/graham_scan.md | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/contents/graham_scan/graham_scan.md b/contents/graham_scan/graham_scan.md
index 18889ce1c..a28e7b2b8 100644
--- a/contents/graham_scan/graham_scan.md
+++ b/contents/graham_scan/graham_scan.md
@@ -23,7 +23,7 @@ We can find whether a rotation is counter-clockwise with trigonometric functions
 {% sample lang="py" %}
 [import:4-6, lang:"python"](code/python/grahamScan.py)
 {% sample lang="go" %}
-[import:13-15, lang:"golang"](code/golang/graham.go)
+[import:13-15, lang:"go"](code/golang/graham.go)
 {% endmethod %}
 
 If the output of this function is 0, the points are collinear.
@@ -49,7 +49,7 @@ In the end, the code should look something like this:
 {% sample lang="py" %}
 [import:14-27, lang:"python"](code/python/grahamScan.py)
 {% sample lang="go" %}
-[import:21-42, lang:"golang"](code/golang/graham.go)
+[import:21-42, lang:"go"](code/golang/graham.go)
 {% endmethod %}
 
 ### Bibliography
@@ -70,7 +70,7 @@ In the end, the code should look something like this:
 {% sample lang="py" %}
 [import, lang:"python"](code/python/grahamScan.py)
 {% sample lang="go" %}
-[import, lang:"golang"](code/golang/graham.go)
+[import, lang:"go"](code/golang/graham.go)
 {% endmethod %}
 
 <script>

From 47e8350489f5eadd22732dfb611c4125e9176b41 Mon Sep 17 00:00:00 2001
From: Julian <jb@futureplay.de>
Date: Wed, 10 Oct 2018 09:14:28 +0200
Subject: [PATCH 3/3] remove merge marker

---
 contents/graham_scan/graham_scan.md | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/contents/graham_scan/graham_scan.md b/contents/graham_scan/graham_scan.md
index 81830fe48..65402dcf2 100644
--- a/contents/graham_scan/graham_scan.md
+++ b/contents/graham_scan/graham_scan.md
@@ -23,13 +23,9 @@ We can find whether a rotation is counter-clockwise with trigonometric functions
 {% sample lang="py" %}
 [import:4-6, lang:"python"](code/python/grahamScan.py)
 {% sample lang="go" %}
-<<<<<<< HEAD
 [import:13-15, lang:"go"](code/golang/graham.go)
-=======
-[import:13-15, lang:"golang"](code/golang/graham.go)
 {% sample lang="java" %}
 [import:27-29, lang:"java"](code/java/GrahamScan.java)
->>>>>>> c50435c03befbc9ca100b67441e2b4aa9f2e0b46
 {% endmethod %}
 
 If the output of this function is 0, the points are collinear.
@@ -55,13 +51,9 @@ In the end, the code should look something like this:
 {% sample lang="py" %}
 [import:14-27, lang:"python"](code/python/grahamScan.py)
 {% sample lang="go" %}
-<<<<<<< HEAD
 [import:21-42, lang:"go"](code/golang/graham.go)
-=======
-[import:21-42, lang:"golang"](code/golang/graham.go)
 {% sample lang="java" %}
 [import:35-70, lang:"java"](code/java/GrahamScan.java)
->>>>>>> c50435c03befbc9ca100b67441e2b4aa9f2e0b46
 {% endmethod %}
 
 ### Bibliography
@@ -82,13 +74,9 @@ In the end, the code should look something like this:
 {% sample lang="py" %}
 [import, lang:"python"](code/python/grahamScan.py)
 {% sample lang="go" %}
-<<<<<<< HEAD
 [import, lang:"go"](code/golang/graham.go)
-=======
-[import, lang:"golang"](code/golang/graham.go)
 {% sample lang="java" %}
 [import, lang:"java"](code/java/GrahamScan.java)
->>>>>>> c50435c03befbc9ca100b67441e2b4aa9f2e0b46
 {% endmethod %}
 
 <script>