fullJustify.go

/* https://leetcode.com/problems/text-justification/
Given an array of words and a width maxWidth,
format the text such that each line has exactly maxWidth 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 maxWidth 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.

Note:

	A word is defined as a character sequence consisting of
	non-space characters only.
	Each word's length is guaranteed to be greater than 0 and
	not exceed maxWidth.
	The input array words contains at least one word.

Example 1:

	Input:
	words = ["This", "is", "an", "example", "of", "text", "justification."]
	maxWidth = 16
	Output:
	[
	"This    is    an",
	"example  of text",
	"justification.  "
	]

Example 2:

	Input:
	words = ["What","must","be","acknowledgment","shall","be"]
	maxWidth = 16
	Output:
	[
	"What   must   be",
	"acknowledgment  ",
	"shall be        "
	]
	Explanation: Note that the last line is "shall be    " instead of
	 "shall     be",
	 because the last line must be left-justified instead of
	 fully-justified.
	 Note that the second line is also left-justified becase
	 it contains only one word.

Example 3:

	Input:
	words = ["Science","is","what","we","understand","well","enough","to","explain",
			"to","a","computer.","Art","is","everything","else","we","do"]
	maxWidth = 20
	Output:
	[
	"Science  is  what we",
	"understand      well",
	"enough to explain to",
	"a  computer.  Art is",
	"everything  else  we",
	"do                  "
	]
*/

package lstring

func fullJustify(words []string, maxWidth int) []string {
	trans2line := func(start, end int, length int, isLastLine bool) string {
		tmp := make([]byte, maxWidth)

		// length 单词长度和
		count := end - start - 1 // 需要填充的空间数量 == word个数-1
		needFills := make([]int, count)

		// the last line must be left-justified instead of fully-justified
		if !isLastLine {
			needFill := maxWidth - length - count
			if count > 0 {
				idx := 0
				for i := 0; i < needFill; i++ {
					needFills[idx]++
					idx++
					idx = idx % count
				}
			}
		}

		// filling
		idx := 0
		for i := start; i < end; i++ {
			word := words[i]
			for j := 0; j < len(word); j++ {
				tmp[idx] = word[j]
				idx++
			}
			if idx < maxWidth {
				tmp[idx] = ' '
				idx++
				for j := 0; idx < maxWidth && i-start < len(needFills) && j < needFills[i-start]; j++ {
					tmp[idx] = ' '
					idx++
				}
			}
		}
		for ; idx < maxWidth; idx++ {
			tmp[idx] = ' '
		}

		return string(tmp)
	}

	res := []string{}
	lineStartIdx, length := 0, len(words[0])
	for i := 1; i < len(words); i++ {
		word := words[i]
		length += len(word)
		if curLength := length + (i - lineStartIdx); curLength > maxWidth {
			// 处理上一行
			line := trans2line(lineStartIdx, i, length-len(word), false)
			res = append(res, line)
			lineStartIdx, length = i, len(word)
			continue
		}
	}

	// last line
	line := trans2line(lineStartIdx, len(words), length, true)
	res = append(res, line)

	return res
}