From b3be6031be628730433ef0df235b12f72213d0c6 Mon Sep 17 00:00:00 2001
From: Dustin Pianalto <dustin@djpianalto.com>
Date: Tue, 1 Sep 2020 09:05:34 -0800
Subject: [PATCH] Problem 4

---
 problem4.go | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 problem4.go

diff --git a/problem4.go b/problem4.go
new file mode 100644
index 0000000..4e04750
--- /dev/null
+++ b/problem4.go
@@ -0,0 +1,47 @@
+package main
+
+import (
+	"log"
+	"math"
+)
+
+func separate(s []int) int {
+	j := 0
+	for i, val := range s {
+		if val <= 0 {
+			s[i] = s[j]
+			s[j] = val
+			j += 1
+		}
+	}
+	return j
+}
+
+func findMissingPositive(s []int) int {
+	l := len(s)
+	for _, val := range s {
+		fval := float64(val)
+		if int(math.Abs(fval)-1) < l && s[int(math.Abs(fval)-1)] > 0 {
+			s[int(math.Abs(fval)-1)] = -s[int(math.Abs(fval)-1)]
+		}
+	}
+
+	for i, val := range s {
+		if val > 0 {
+			return i + 1
+		}
+	}
+	return l + 1
+}
+
+func FindMissing(s []int) int {
+	shift := separate(s)
+	return findMissingPositive(s[shift:])
+}
+
+func main() {
+	s := []int{3, 4, -1, 1}
+	log.Println(FindMissing(s))
+	s = []int{1, 2, 0}
+	log.Println(FindMissing(s))
+}