替换空格

请实现一个函数，将一个字符串中的空格替换成“%20”。
例如，当字符串为We Are Happy.则经过替换之后的字符串为We%20Are%20Happy

class Solution():
    def replaceblank(array):
        count = 0
        for i in range(array):
            if i == " ":
                count += 1
        
        newlength = len(array) + count * 2
        i = j = 0
        while i < len(array) and j < len(newlength):
            if array[i] == " ":
                newlength[j] = "2"
                j += 1
                newlength[j] = "0"
                j += 1
                newlength[j] = "%"
                j += 1
                i += 1
            else:
                newlength[j] = array[i]
        return newlength

package problem004
func replaceSpace(str []byte, length int) {
    count := 0
    // 遍历一遍字符串， 统计字符出现的数目, 计算替换后的字符串长度
    for i:=0; i<length; i++ {
        if str[i] == ' '{
            count++
        }
    }
    newlength := length + count*2

    // 两个index，一个指向length-1, 另一个指向newlength-1，遍历一遍字符串，完成替换
    for l,nl := length-1,newlength-1; l>=0 && nl>=0; {
        if str[l]==' '{
            str[nl] = '0'
            nl--
            str[nl] = '2'
            nl--
            str[nl] = '%'
            nl--
            l--
        } else {
            str[nl] = str[l]
            nl--
            l--
        }
    }
}