Reverse Words in a String | LeetCode 151 | C++, Java, Python

Ultimate i would say hats off sir👌👌👏👏

what is the point of writing 7th line python . when we placed a condition i<n

class Solution(object):
def reverseWords(self, s):
sp = s.strip().split()
res = ""
i,j=0,len(sp)-1
while i<j:
sp[i],sp[j]=sp[j],sp[i]
i+=1
j-=1
return " ".join(sp)

EASIEST SOLUTION C++ NO EXTRA SPACE

string revWords(string s) {

int i=0;
while(i<s.size() && s[i]==' ')
{
i++;
}

int j=s.size()-1;
while(j>=0 && s[j]==' ')
{
j--;
}


int cnt=0;
string ans="";
string res="";



for(int x=i;x<=j;x++)
{
if(s[x]==' ')
{
cnt++;
continue;
}
if(cnt)
{
if(res=="")
{
res=ans;
}
else
{
res=ans+" "+res;
}
cnt=0;
ans="";
}
ans+=s[x];
}
res=ans+" "+res;
return res;
}

I write a main method after your code. and it doesn't work. It only returns one word of my sentence.

public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);


System.out.println("Enter the sentence:");
String sentence = keyboard.next();
String result = reverseWords(sentence);
System.out.println(result);

}
Did I do anything wrong with my main method?

thanks for the explanation!!

Awesome explaination !!

best video i have found on how to reverse an word
thank u sir...

Sir it is difficult for Me to understand the concept why we take subs from (i, j-i) why not from (i,j) in c++

How to skip last two words in sentence?

My input string is: Hi there. My name is Kalp. This is my lucky day. I like coding so much. This is it.

Expected output is: Hi there. name My is Kalp. my is This lucky day. coding like I so much. This is it.

Code for no extra space
class Solution {
public:
string reverseWords(string s) {
int k=s.size();
int n=k;
s+=" ";
while(n>=0)
{
while(n>=0 && s[n]==' ')
{
n--;
}
if(n<0) break;
int j=n-1;
while(j>=0 && s[j]!=' ')
{
j--;
}
s+=s.substr(j+1,n-j)+" ";
n=j-1;
}
s=s.substr(k+1,s.size()-(k+2));
return s;
}
};

While(i<n&&s[i]==' '){
i++;
}
Why is it giving empty character constant error and empty expression error . Please tell . I have written the code exactly like u but it doesn't run

This isn't working for me.
The output is:
"blue is sky the the"
"world hello hello"
"example good a a".

The output always duplicate the last word.

Edit*
Never mind, I miss-placed the i = j + 1 into the final else statement

I REALLY LIKED THE PART WHERE HE EXPLAINED THE CODE IN C++ AND PYTHON

commented using API.

video are very helpful.

s = sentence.split()[::-1]
l = []
for i in s:
l.append(i[::-1])
print('-'.join(l))

Thank you, was very helpful

Good video sir,
Can you write this Java program too:
Input: "This is, the most; particular example!"
Output: "example particular, most the; is This!"

I don't understand why we can't just use trim in java and strip in python to get rid of the leading and trailing spaces.

thanks.........

How to write complext code 101

can anyone tell what is the significance of writing if(i>=n)break; here?
it will be really helpful

public static void test2() {
String str = " My name is Aman ";
StringBuilder strb = new StringBuilder(str);
String str2 = strb.reverse().toString();

int i=0; int j=0;
while(i<str2.length() && str2.charAt(i)==' ') {
i++;
}
String str3="";
while(j<str2.length()) {
j=i;
while(i<str2.length() && str2.charAt(i)!=' ') {
i++;
}

StringBuilder strb1 = new StringBuilder(str2.substring(j, i));
str3=str3+" "+strb1.reverse().toString();
i++;
System.out.println(str3);
}
System.out.println(str3);
}

always try to show runtime speed and space after code is submitted

thank you bro, your explanations are so clear

In Leetcode, it gives error for Python3

Time Limit Exceeded

this code is not working in leetcode

Your vedios are really great. In this solution, we append and then copy result string in every iteration which is not optimal, TC will become O(n^2). It is better to start from end of input string, reverse each sub-string and then append it to result string, this will give us TC as O(n)

Thanku sir

Hi @Abhishek the video is very good, but I am thinking can we split the string using spaces and rearranging in the reverse order it will do our requirement right.

C++ Code is not working

Thanks

please provide the desired code in description box

Thank You Sir.

python
class Solution:
def reverseWords(self, s: str) -> str:
return " ".join(list(filter(lambda x: len(x)>0,s.split(" ")))[::-1])

I am wondering can we use stringtok in this question? Yes, it will be space O(n) but can be solved quicker I guess!

Code is not reversing , please help

Perfect

Nice explanation

Nice explanation. Although I was expecting in-place solution.

Jaduu!

If you need O(1) space sol:

class Solution {
public:
void reverseword(string &s, int i, int j){ //reverse string from i to j
while(i<j){
char t = s[i];
s[i++] = s[j];
s[j--] = t;
}
}
string reverseWords(string s) {
int i=0, j=0;
int l=0;
int len = s.size();

int wordcount = 0;

while(true){
while(i<len && s[i] == ' ') //skip spaces in front
i++;
if(i==len)
break;
if(wordcount) //add space between the middle words
s[j++] = ' ';
l=j;
while(i<len && s[i] != ' '){ //place the word at the starting, removing spaces
s[j] = s[i];
j++, i++;
}
reverseword(s,l,j-1); //reverse word
wordcount++;
}
s.resize(j); //resize s to smaller string after removing spaces
reverse(s.begin(), s.end()); //Finally, reverse entire string to get the result
return s;
}
};

Wow man... Quality content every time

Thank you. You did in a very clear way.

Really you are the best!. Especially those python solutions

Excellent explanation

Time complexity should be
O(n) We are still iterating through the array linearly, and when the j loop is activated,
it still linearly searches in the same array but when it reaches a letter/nospace until it reaches '_' (_ is 1 space). , then continues from outer main loop again, the inner loop if it satisfies the condition all the way to the end of len(array).

Space should be
O(n) since we create a result array, it cannot be O(1) because we are not manipulating the input array in place.

Please feel free to correct me if I'm wrong but I am thinking this is correct.

Sir, there's no doubt that you make a problem look very easy but it will be great if you write code in C language also...plzzzzz

Excellent
Thank you very much
Changing the index value after spaces is like magic
Really awesome 😎