[2700][1A] CF1617E 结论题 建模 树的直径

Author: EndlessCheng

main/1600-1699/1617E.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"bufio"
+	. "fmt"
+	"io"
+	"math/bits"
+)
+
+// github.com/EndlessCheng/codeforces-go
+func f(v, w uint) (c int) {
+	for v != w {
+		if v < w {
+			v, w = w, v
+		}
+		v = 1<<bits.Len(v-1) - v
+		c++
+	}
+	return
+}
+
+func CF1617E(_r io.Reader, out io.Writer) {
+	in := bufio.NewReader(_r)
+	var n, p, q int
+	Fscan(in, &n)
+	a := make([]uint, n)
+	for i := range a {
+		Fscan(in, &a[i])
+	}
+
+	mx := -1
+	for i := 1; i < n; i++ {
+		c := f(a[i], a[0])
+		if c > mx {
+			mx, p = c, i
+		}
+	}
+
+	mx = -1
+	for i, v := range a {
+		if i != p {
+			c := f(v, a[p])
+			if c > mx {
+				mx, q = c, i
+			}
+		}
+	}
+	Fprint(out, p+1, q+1, mx)
+}
+
+//func main() { CF1617E(os.Stdin, os.Stdout) }

main/1600-1699/1617E_test.go

@@ -0,0 +1,24 @@
+package main
+
+import (
+	"github.com/EndlessCheng/codeforces-go/main/testutil"
+	"testing"
+)
+
+// https://codeforces.com/problemset/problem/1617/E
+// https://codeforces.com/problemset/status/1617/problem/E
+func TestCF1617E(t *testing.T) {
+	// just copy from website
+	rawText := `
+inputCopy
+5
+5 6 7 8 9
+outputCopy
+2 5 5
+inputCopy
+2
+4 8
+outputCopy
+1 2 2`
+	testutil.AssertEqualCase(t, rawText, 0, CF1617E)
+}