Merge pull request #2105 from a93a/main

Create 0402-remove-k-digits.kt

Author: a93a

kotlin/0402-remove-k-digits.kt

@@ -0,0 +1,18 @@
+class Solution {
+    fun removeKdigits(num: String, k: Int): String {
+        val stack = Stack<Char>() //monotonic stack 
+        var count = k
+        for(i in 0 until num.length){
+            while(count > 0 && !stack.isEmpty() && num[i] < stack.peek()){
+                stack.pop() //remove the larger int
+                count--
+            }
+            stack.push(num[i])
+        } 
+        repeat(count){ //pop the last k integers (largest integers)
+            stack.pop()
+        }
+        val sum = stack.joinToString("")
+        return if(sum == "") "0" else sum.toBigInteger().toString() //to int to remove all leading Zeros, instead of using Strinbuilder
+    }
+}