[1900][1A] CF708B 构造

main/700-799/708B.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	. "fmt"
+	"io"
+	"math"
+	"strings"
+)
+
+// https://space.bilibili.com/206214
+func CF708B(in io.Reader, out io.Writer) {
+	var c00, c01, c10, c11 int
+	Fscan(in, &c00, &c01, &c10, &c11)
+	f := func(c int) int {
+		x := (1 + int(math.Sqrt(float64(1+8*int64(c))))) / 2
+		if x*(x-1)/2 == c {
+			return x
+		}
+		return -1
+	}
+	c0, c1 := f(c00), f(c11)
+	if c0 < 0 || c1 < 0 {
+		Fprint(out, "Impossible")
+		return
+	}
+
+	if c01 == 0 && c10 == 0 {
+		if c00 > 0 && c11 > 0 {
+			Fprint(out, "Impossible")
+		} else if c11 == 0 {
+			Fprint(out, strings.Repeat("0", c0))
+		} else {
+			Fprint(out, strings.Repeat("1", c1))
+		}
+		return
+	}
+
+	if c01+c10 != c0*c1 {
+		Fprint(out, "Impossible")
+		return
+	}
+	left1, right0 := c10/c0, c10%c0
+	ans := strings.Repeat("1", left1) + strings.Repeat("0", c0-right0)
+	if right0 > 0 {
+		ans += "1" + strings.Repeat("0", right0)
+		c1--
+	}
+	ans += strings.Repeat("1", c1-left1)
+	Fprint(out, ans)
+}
+
+//func main() { CF708B(os.Stdin, os.Stdout) }

main/700-799/708B_test.go

@@ -0,0 +1,26 @@
+package main
+
+import (
+	"github.com/EndlessCheng/codeforces-go/main/testutil"
+	"testing"
+)
+
+// https://codeforces.com/problemset/problem/708/B
+// https://codeforces.com/problemset/status/708/problem/B
+func TestCF708B(t *testing.T) {
+	// just copy from website
+	rawText := `
+inputCopy
+1 2 3 4
+outputCopy
+Impossible
+inputCopy
+1 2 2 1
+outputCopy
+0110
+inputCopy
+3 8 4 6
+outputCopy
+1001011`
+	testutil.AssertEqualCase(t, rawText, 0, CF708B)
+}