💯【算法面试】Go题解 13.替换空格

func replaceSpace(s string) string {
    return strings.ReplaceAll(s, " ", "%20")
}

// Replace returns a copy of the string s with the first n
// non-overlapping instances of old replaced by new.
// If old is empty, it matches at the beginning of the string
// and after each UTF-8 sequence, yielding up to k+1 replacements
// for a k-rune string.
// If n < 0, there is no limit on the number of replacements.
func Replace(s, old, new string, n int) string {
	if old == new || n == 0 {
		return s // avoid allocation
	}

	// Compute number of replacements.
	if m := Count(s, old); m == 0 {
		return s // avoid allocation
	} else if n < 0 || m < n {
		n = m
	}

	// Apply replacements to buffer.
	var b Builder
	b.Grow(len(s) + n*(len(new)-len(old)))
	start := 0
	for i := 0; i < n; i++ {
		j := start
		if len(old) == 0 {
			if i > 0 {
				_, wid := utf8.DecodeRuneInString(s[start:])
				j += wid
			}
		} else {
			j += Index(s[start:], old)
		}
		b.WriteString(s[start:j])
		b.WriteString(new)
		start = j + len(old)
	}
	b.WriteString(s[start:])
	return b.String()
}


// ReplaceAll returns a copy of the string s with all
// non-overlapping instances of old replaced by new.
// If old is empty, it matches at the beginning of the string
// and after each UTF-8 sequence, yielding up to k+1 replacements
// for a k-rune string.
func ReplaceAll(s, old, new string) string {
	return Replace(s, old, new, -1)
}

b.WriteString(s[start:j]) //start标记从旧字符串的哪个位置开始
b.WriteString(new) //写入替换数据
start = j + len(old) //移动start