Text_Justification.py

"""
Given an array of words and a length L, format the text such that each line has exactly L characters and is fully (left and right) justified.

You should pack your words in a greedy approach; that is, pack as many words as you can in each line. Pad extra spaces ' ' when necessary so that each line has exactly L characters.

Extra spaces between words should be distributed as evenly as possible. If the number of spaces on a line do not divide evenly between words, the empty slots on the left will be assigned more spaces than the slots on the right.

For the last line of text, it should be left justified and no extra space is inserted between words.

For example,
words: ["This", "is", "an", "example", "of", "text", "justification."]
L: 16.

Return the formatted lines as:
[
   "This    is    an",
   "example  of text",
   "justification.  "
]
Note: Each word is guaranteed not to exceed L in length.
"""

class Solution:
    # @param words, a list of strings
    # @param L, an integer
    # @return a list of strings
    def fullJustify(self, words, L):
        cur_len = 0
        res = []
        ret = []
        for word in words:
            if cur_len + len(word) + len(res) <= L:
                res.append(word)
                cur_len += len(word)
            else:
                if len(res) == 1:
                    ret.append(self.fill_spaces(res[0], L))
                else:
                    extra_spaces = L - cur_len - (len(res) - 1)
                    each_extra = extra_spaces / (len(res) - 1) + 1
                    rest_spaces = extra_spaces % (len(res) - 1)
                    for i in range(rest_spaces):
                        res[i] += ' '
                    line = (' ' * each_extra).join(res)
                    ret.append(line)
                res = []
                res.append(word)
                cur_len = len(word)
        ret.append(self.fill_spaces(' '.join(res), L))
        return ret

    def fill_spaces(self, string, L):
        length = len(string)
        string += ' ' * (L - length)
        return string

    # Notice:
    # 1. 算extra_spaces的时候是len(res) - 1
    # 2. 在each extra的后面+1算上必有的space
    # 3. 可以用for循环做, 但是别忘了最后要reset res, cur_len
    # 4. 最后是一定会append多余的一行的, line 49没必要再check了, 直接append
    # 5. 把fill_space函数单独提出来比较合适
    # 6. Line 42 43 这里的思想要记住, 比较重要