65.YA

def solve(arr: list) -> str:
    def reverse(left, right):
        while left < right:
            arr[left], arr[right] = arr[right], arr[left]
            left += 1
            right -= 1

    left = 0

    for right in range(len(arr)):
        if arr[right] == ' ':
            reverse(left, right - 1)
            left = right + 1

    reverse(left, right)

    return "".join(arr)