Added solution for word reverse.

anxious-coder-lhs · anxious-coder-lhs · commit f7a347a5dbbb · 2020-11-06T17:38:14.000+05:30
diff --git a/README.md b/README.md
@@ -56,6 +56,7 @@ Happy to accept any contributions to this in any langugage.
 21. [Leet Code 1239 - Maximum length of the unique character string](https://leetcode.com/problems/maximum-length-of-a-concatenated-string-with-unique-characters/) | [Solution](./level_medium/LeetCode_1239_MaxLength.ts)
 22. [Leet Code 445 - Add Numbers II](https://leetcode.com/problems/add-two-numbers-ii/) | [Solution 1](./level_medium/LeetCode%20445_Add%202%20Numbers_1.ts) | [Solution 2](./level_medium/LeetCode%20445_Add%202%20Numbers_2.ts)
 23. [Leet Code 59 - Spiral Matrix II](https://leetcode.com/problems/spiral-matrix-ii/) | [Solution](level_medium/SpiralMatrixII.ts)
+24. [Leet Code 151 - Reverse Words in a String](https://leetcode.com/problems/reverse-words-in-a-string/) | [Solution](level_medium/LeetCode_151_Reverse_Words_In_a_String.ts)
 
 
 
diff --git a/level_medium/LeetCode_151_Reverse_Words_In_a_String.ts b/level_medium/LeetCode_151_Reverse_Words_In_a_String.ts
@@ -0,0 +1,38 @@
+/**
+ * Leet Code 151
+ * 
+ * Solution uses an approach to add words in a stack as we do a single iteration. Adding words with the space
+ * boundaries are done via slicing the string from the position to position. Altrnatively, this can also be done
+ * using concatenation as well.
+ * 
+ * Once the words are in the stack, they are pulled out to form a string in reverse order.
+ * 
+ * Time: O(n) since each element is visited once, and O(n) space since additional storage of stack is used.
+ * 
+ * @param s 
+ */
+function reverseWords(s: string): string {
+    const stack: string[] = []
+    
+    // Add all the items to a stack.
+    let start = 0, end  = 0;
+    for (let idx = 0; idx < s.length; idx++) {
+        if (s[idx] === " ") {
+            if (start !== end) stack.push(s.slice(start, end));
+            start = idx + 1, end = idx + 1;
+        } else {
+            end++;
+        }
+    }
+    
+    // Adding last word
+    if (start !== end) stack.push(s.slice(start, end));
+    
+    // Reverse the items as a string.
+    let result = stack.pop(), substr: string | undefined = ""
+    while( (substr = stack.pop()) !== undefined) {
+        result += " " + substr
+    }
+    
+    return result || "";
+};
