Create ReverseWordInAString.md

Competitive_Programming/C++/String/ReverseWordInAString.md

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+ Reverse word in a String
+
+Input: s = "a good example"
+
+Output: "example good a"
+
+Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.
+
+## 1st Approach 
+
+- In this approach , first we will reverse the given string .
+- then we have to split the string using istringstream .
+- then simply start the for each word we will reverse the word and it to the resultant string.
+- to reverse function in c++ takes O(n) time complexity.
+
+``` c++
+    string reverseWords(string s) {
+        reverse(s.begin(), s.end());
+        string word, result;
+        istringstream iss(s);
+
+        while (iss >> word) {
+            reverse(word.begin(), word.end());
+            result += word + " ";
+        }
+
+        result.pop_back();
+        return result;
+    }
+    int main(){
+        string st;
+        cin >> st;
+        cout << reverseWords ( st );
+        return 0;
+    }
+```
+>Input: s = "a good example"
+>
+>Output: "example good a"
+
+> Time Complexity O(n*m) n is number of words in the string ; m is the alphabets in each word.
+>
+>Space Complexity O(n)
+
+## 2nd Approach
+
+### Using Stack
+
+- In this approch , we will store the word in stack and when we have traverse the full string .
+- then we will store the top word in resulting string and then pop.
+- we will do this till the stack doesnot turn empty.
+
+**We have used stack as it works on principle of first in last out.** 
+``` c++
+    string reverseWords(string s) {
+        stack<string> words;
+
+        istringstream iss(s);
+        string word;
+        while (iss >> word) {
+            words.push(word);
+        }
+
+        string result = "";
+        for (; !words.empty(); words.pop()) {
+            result += words.top() + " ";
+        }
+
+        result.pop_back();
+        return result;
+    }
+    int main(){
+        string st;
+        cin >> st;
+        cout << reverseWords ( st );
+        return 0;
+    }
+```
+>Input: s = "a good example"
+>
+>Output: "example good a"
+
+>Time Complexity : O(n) , where n is the number of words in the string.
+>Space Complexity: O(n) , as we are using stack 
+