leetcode 151. https://leetcode.com/problems/reverse-words-in-a-string/
Example 1:
Input: "the sky is blue" Output: "blue is sky the"
Example 2:
Input: " hello world! " Output: "world! hello" Explanation: Your reversed string should not contain leading or trailing spaces.
Example 3:
The INPUT: "A Good Example" the Output: "A Good Example" Explanation: Multiple Spaces by You need to the reduce the BETWEEN TWO words to A SINGLE at The Space in the reversed String.
The basic idea is, first reverse the entire string, then reverse each word. Handle extra spaces in the process. In-place algorithm
class Solution {
public:
string reverseWords(string s) {
// reverse whole string
reverse(s.begin(), s.end());
// reverse each word
int i = 0,j = 0, storedIndex = 0;
while (i < s.size()){
// put i to the first letter of a word
while (i < s.size() && s[i] == ' ') ++i;
// add a space if this is not the first and last word
if (i < s.size() && storedIndex != 0) s[storedIndex++] = ' ';
j = i;
// put j to the end of the word
while (j < s.size() && s[j] != ' ') ++j;
// reverse this word. There may be spaces in front of the word, and after reverse it goes to the end.
// if s contains only space, i == j, reverse will do nothing
reverse(s.begin()+storedIndex, s.begin()+j);
// put stored index to the end of the word
storedIndex += j - i;
// put i to the start of next search
i = j;
}
// finally, storedIndex will point to the letter next to the last word
s.erase(s.begin()+storedIndex, s.end());
return s;
}
};