LeetCode 1324. 竖直打印单词

示例 1：
输入：s = "HOW ARE YOU"
输出：["HAY","ORO","WEU"]
解释：每个单词都应该竖直打印。 
 "HAY"
 "ORO"
 "WEU"
 
示例 2：
输入：s = "TO BE OR NOT TO BE"
输出：["TBONTB","OEROOE","   T"]
解释：题目允许使用空格补位，但不允许输出末尾出现空格。
"TBONTB"
"OEROOE"
"   T"

示例 3：
输入：s = "CONTEST IS COMING"
输出：["CIC","OSO","N M","T I","E N","S G","T"]
 
提示：
1 <= s.length <= 200
s 仅含大写英文字母。
题目数据保证两个单词之间只有一个空格。

class Solution {
public:
    vector<string> printVertically(string s) {
    	vector<int> idx;
        s.push_back(' ');
    	int i, n = s.size();
    	char prev = ' ';
    	for(i = 0; i < n; ++i)
    	{
    		if(prev==' ' && s[i] != ' ')
    			idx.push_back(i);//每个单词起点
    		prev = s[i];
    	}
    	vector<string> ans;
    	string str;
    	while(1)
    	{
    		str = "";
    		for(i = 0; i < idx.size(); ++i)
    		{
    			if(idx[i] != -1)//下标不为-1
    			{
    				str += s[idx[i]++];//拼接字符，下标+1
    				if(s[idx[i]] == ' ')//+1后为空字符
    					idx[i] = -1;//置为-1
    			}
    			else
    				str += ' ';//为-1的话，补空格
    		}
    		while(!str.empty() && str.back()==' ')
    			str.pop_back();//删除尾部空格
    		if(str == "")
    			break;//字符串空，说明，全部到达末尾，结束
    		else
    			ans.push_back(str);
    	}
    	return ans;
    }
};