20201111: sf

20201111/main.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"math/rand"
+)
+
+func main() {
+	r := rand.Intn(100)
+	fmt.Println("r:", r)
+	var src []int
+	for i := 0; i < 100; i++ {
+		src = append(src, i)
+		if i == r {
+			continue
+		}
+		src = append(src, i)
+	}
+	n, _ := findSingleNumber(src)
+	fmt.Println("lost number:", n)
+	n, _ = findSingleNumber2(src)
+	fmt.Println("lost number2:", n)
+	n, _ = findSingleNumber3(src)
+	fmt.Println("lost number3:", n)
+}
+
+func findSingleNumber(src []int) (int, error) {
+	m := map[int]int{}
+	for _, n := range src {
+		m[n] += 1
+	}
+	for k, v := range m {
+		if v == 1 {
+			return k, nil
+		}
+	}
+	return 0, errors.New("not found")
+}
+
+func findSingleNumber2(src []int) (int, error) {
+	m := map[int]struct{}{}
+	for _, n := range src {
+		if _, ok := m[n]; ok {
+			delete(m, n)
+		} else {
+			m[n] = struct{}{}
+		}
+	}
+	for k := range m {
+		return k, nil
+	}
+	return 0, errors.New("not found")
+}
+
+func findSingleNumber3(src []int) (int, error) {
+	num := 0
+	for _, n := range src {
+		num = num ^ n
+	}
+	if num == 0 {
+		return 0, errors.New("not found")
+	}
+	return num, nil
+}