02.2 go fast, O(N*M)

02/02.go

@@ -5,7 +5,6 @@ import (
 	"os"
 	"strconv"
 	"strings"
-	"slices"
 )
 
 func SplitByLines(bytes []byte) []string {
@@ -13,46 +12,100 @@ func SplitByLines(bytes []byte) []string {
 }
 
 func Less(a, b int) bool {
-	return a<b
+	return a < b
 }
 func More(a, b int) bool {
-	return a>b
+	return a > b
 }
-func P(f func (int, int) bool, a, b int) bool {
-	return f(a, b) && Abs(a-b)<=3
+func P(f func(int, int) bool, a, b int) bool {
+	return f(a, b) && Abs(a-b) <= 3
 }
 func Abs(x int) int {
-	if x<0 {
+	if x < 0 {
 		x = -x
 	}
 	return x
 }
-func Safe1(l []int, j, e int) bool {
+func Safe1(l []int) bool {
+	if l[0] == l[1] {
+		return false
+	}
 	f := Less
-	if l[j-1]>l[j] { f = More }
-	for j<e && P(f, l[j-1], l[j]){
+	if l[0] > l[1] {
+		f = More
+	}
+	j := 1
+	for j < len(l) && P(f, l[j-1], l[j]) {
 		j++
 	}
-	r := j<e
+	r := j < len(l)
 	return !r
 }
 func Safe2(l []int) bool {
-	if l[0]==l[1] { return false }
-	f := Less
-	if l[0]>l[1] { f = More }
-	c := 0
-	j := 2
-	for j<len(l) && c<2 {
-		if !(P(f, l[j-1], l[j])) && (P(f, l[j-2], l[j])) { 
-			c++ 
+	cl := 0
+	cm := 0
+	cq := 0
+	il := -1
+	im := -1
+	iq := -1
+	for i := 1; i < len(l); i++ {
+		a := l[i-1]
+		b := l[i]
+		if a >= b {
+			cl++
+			if il == -1 {
+				il = i
+			}
+		}
+		if a <= b {
+			cm++
+			if im == -1 {
+				im = i
+			}
+		}
+		if Abs(a-b) > 3 {
+			cq++
+			if iq == -1 {
+				iq = i
+			}
 		}
-		j++
 	}
-	return c<2
+	if cq == 0 && (cm == 0 || cl == 0) {
+		return true
+	}
+	if cq > 2 || cl > 2 && cm > 2 {
+		return false
+	}
+	if cq == 2 {
+		return Safe1(Skip(l, iq))
+	}
+	if iq != -1 {
+		return Safe1(Skip(l, iq)) || Safe1(Skip(l, iq-1))
+	}
+	if 0 < cl && cl <= 2 {
+		return Safe1(Skip(l, il)) || Safe1(Skip(l, il-1))
+	}
+	if 0 < cm && cm <= 2 {
+		return Safe1(Skip(l, im)) || Safe1(Skip(l, im-1))
+	}
+	return false
+}
+func Skip(l []int, i int) []int {
+	n := make([]int, len(l)-1)
+	k := 0
+	for j, x := range l {
+		if j != i {
+			n[k] = x
+			k++
+		}
+	}
+	return n
 }
 func main() {
 	bytes, err := os.ReadFile("./input.txt")
-	if err != nil { panic(err) }
+	if err != nil {
+		panic(err)
+	}
 	lines := SplitByLines(bytes)
 	data := make([][]int, len(lines))
 	for i, l := range lines {
@@ -66,24 +119,16 @@ func main() {
 	}
 	s := 0
 	for _, l := range data {
-		if Safe1(l, 1, len(l)) { s++ }
+		if Safe1(l) {
+			s++
+		}
 	}
 	fmt.Println(s)
 	s = 0
 	for _, l := range data {
-		t := make([]int, len(l))
-		copy(t, l)
-		t = slices.Delete(t, 1, 2)
-		if Safe1(l, 1, len(l)) || 
-			Safe1(l, 2, len(l)) || 
-			Safe1(t, 1, len(t)) || 
-			Safe1(l, 1, len(l)-1) {
-			s++ 
-		} else if Safe2(l) { 
-			fmt.Println(l)
+		if Safe2(l) {
 			s++
 		}
 	}
 	fmt.Println(s)
-	println(len(data))
 }