算法

import (
	"fmt"
	"strings"
)

func main(){
	fmt.Println(Utf8Index("北京天安门最美丽", "天安门"))
	fmt.Println(strings.Index("北京天安门最美丽", "男"))
	fmt.Println(strings.Index("", "男"))
	fmt.Println(Utf8Index("12ws北京天安门最美丽", "天安门"))
}

func Utf8Index(str, substr string) int {
	asciiPos := strings.Index(str, substr)
	if asciiPos == -1 || asciiPos == 0 {
		return asciiPos
	}
	pos := 0
	totalSize := 0
	reader := strings.NewReader(str)
	for _, size, err := reader.ReadRune(); err == nil; _, size, err = reader.ReadRune() {
		totalSize += size
		pos++
		// 匹配到
		if totalSize == asciiPos {
			return pos
		}
	}
	return pos
}

这题不会做…

package main

import "sync"

// 实现一个单例

type singleton struct{}

var ins *singleton
var mu sync.Mutex

//懒汉加锁:虽然解决并发的问题，但每次加锁是要付出代价的
func GetIns() *singleton {
	mu.Lock()
	defer mu.Unlock()

	if ins == nil {
		ins = &singleton{}
	}
	return ins
}

//双重锁:避免了每次加锁，提高代码效率
func GetIns1() *singleton {
	if ins == nil {
		mu.Lock()
		defer mu.Unlock()
		if ins == nil {
			ins = &singleton{}
		}
	}
	return ins
}

//sync.Once实现
var once sync.Once

func GetIns2() *singleton {
	once.Do(func() {
		ins = &singleton{}
	})
	return ins
}