def ReverseString(s, leftCharIndex, rightCharIndex):
            #base case
            if leftCharIndex >= rightCharIndex:
                return
            #swap the charcters 
            s[leftCharIndex], s[rightCharIndex] = s[rightCharIndex], s[leftCharIndex]
                
            return ReverseString(s, leftCharIndex+1, rightCharIndex-1)

s = ["h","e","l","l","o"]
ReverseString(s, 0, len(s)-1)
print(s)