[Leetcode] 68. Text Justification 解题报告

题目：

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.

click to show corner cases.

Corner Cases:

A line other than the last line might contain only one word. What should you do in this case?

In this case, that line should be left-justified.

思路：

一道纯粹的字符串处理的题目，但是要把代码写的优雅比较困难。我的代码就写的非常长（~~），但是思路比较容易理解：首先将将字符串根据长度加入不同行中；然后对不同行进行调整（调整过程中需要注意字符串个数为1的特殊情况，以及字符串之间的空格序列不递增的原则，这可以通过除数和余数计算），对最后一行还需要做特殊处理。个人非常不喜欢这类题目，没有考察什么高级算法，但是却非常容易搞出bug。

代码：

class Solution {
public:
vector<string> fullJustify(vector<string>& words, int maxWidth)
{
b1d4

vector<string> ret;
vector<int> nums; // number of words in each line
string line;
int num = 0;
for (int i = 0; i < words.size(); ++i) // step 1: add all the words
{
if (canAdd(line, words[i], maxWidth)) // add to current line
{
if (line != "")
line += " ";
line += words[i];
num++;
}
else // add to the next line
{
ret.push_back(line);
nums.push_back(num);
line = "";
num = 0;
i--;
}
}
if (num != 0) // remaining words, so add to the next
{
ret.push_back(line);
nums.push_back(num);
}
int index = 0, i = 0;
vector<int> starts; // index of start word in each line
for (; i < nums.size(); ++i)
{
starts.push_back(index);
index += nums[i];
}

if (ret.size() == 0)
return ret;
for (i = 0; i < ret.size() - 1; ++i) // adjust the word in each line
{
int length = ret[i].length();
if (length < maxWidth) // need to adjust the words
{
int num = nums[i];
if (num == 1)
{
ret[i] += string(maxWidth - length, ' ');
}
else
{
vector<int> spaces(num - 1, 1);
int index = 0;
for (int j = 0; j < maxWidth - length; ++j)
{
spaces[index]++;
index = (index + 1) % (num - 1);
}
ret[i] = "";
index = starts[i];
for (int j = 0; j < num - 1; ++j)
{
ret[i] += words[index++];
ret[i] += string(spaces[j], ' ');
}
ret[i] += words[index++];
}
}
}
if(ret[i].length() < maxWidth) // adjust the last line
ret[i] += string(maxWidth - ret[i].length(), ' ');
return ret;
}
private:
bool canAdd(string &s, string &word, int maxWidth)
{
if(s.length() == 0)
return word.length() <= maxWidth;
if(s.length() + 1 + word.length() <= maxWidth)
return true;
else
return false;
}
};