[1700][1A] CF1148C 分类讨论 交换至有序

Author: EndlessCheng

main/1100-1199/1148C.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"bufio"
+	. "fmt"
+	"io"
+)
+
+// github.com/EndlessCheng/codeforces-go
+func CF1148C(_r io.Reader, _w io.Writer) {
+	in := bufio.NewReader(_r)
+	out := bufio.NewWriter(_w)
+	defer out.Flush()
+
+	var n int
+	Fscan(in, &n)
+	a := make([]int, n+1)
+	p := make([]int, n+1)
+	for i := 1; i <= n; i++ {
+		Fscan(in, &a[i])
+		p[a[i]] = i
+	}
+
+	type pr struct{ x, y int }
+	ans := []pr{}
+	for i := 1; i <= n; i++ {
+		j := p[i]
+		if j == i {
+			continue
+		}
+		sz := len(ans)
+		if j-i >= n/2 {
+			ans = append(ans, pr{i, j})
+			p[a[i]] = j
+		} else if j <= n/2 {
+			ans = append(ans, pr{j, n}, pr{i, n})
+			p[a[i]] = n
+			p[a[n]] = j
+		} else if i <= n/2 {
+			ans = append(ans, pr{1, j}, pr{1, n}, pr{i, n}, pr{1, j})
+			p[a[i]] = n
+			p[a[n]] = j
+		} else {
+			ans = append(ans, pr{1, j}, pr{1, i}, pr{1, j})
+			p[a[i]] = j
+		}
+		for _, p := range ans[sz:] {
+			a[p.x], a[p.y] = a[p.y], a[p.x]
+		}
+	}
+	Fprintln(out, len(ans))
+	for _, p := range ans {
+		Fprintln(out, p.x, p.y)
+	}
+}
+
+//func main() { CF1148C(os.Stdin, os.Stdout) }

main/1100-1199/1148C_test.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"github.com/EndlessCheng/codeforces-go/main/testutil"
+	"testing"
+)
+
+// https://codeforces.com/problemset/problem/1148/C
+// https://codeforces.com/problemset/status/1148/problem/C
+func TestCF1148C(t *testing.T) {
+	// just copy from website
+	rawText := `
+inputCopy
+2
+2 1
+outputCopy
+1
+1 2
+inputCopy
+4
+3 4 1 2
+outputCopy
+4
+1 4
+1 4
+1 3
+2 4
+inputCopy
+6
+2 5 3 1 4 6
+outputCopy
+3
+1 5
+2 5
+1 4`
+	testutil.AssertEqualCase(t, rawText, 0, CF1148C)
+}