Create Build Lowest Number by Removing n digits from a given number

Build Lowest Number by Removing n digits from a given number

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+// C++ program for the above approach
+
+#include <bits/stdc++.h>
+using namespace std;
+
+string removeKdigits(string num, int k)
+{
+	int n = num.size();
+	stack<char> mystack;
+	// Store the final string in stack
+	for (char c : num) {
+		while (!mystack.empty() && k > 0
+			&& mystack.top() > c) {
+			mystack.pop();
+			k -= 1;
+		}
+
+		if (!mystack.empty() || c != '0'){
+			mystack.push(c);
+		}
+	}
+
+	// Now remove the largest values from the top of the
+	// stack
+	while (!mystack.empty() && k--)
+		mystack.pop();
+	if (mystack.empty())
+		return "0";
+
+	// Now retrieve the number from stack into a string
+	// (reusing num)
+	while (!mystack.empty()) {
+		num[n - 1] = mystack.top();
+		mystack.pop();
+		n -= 1;
+	}
+	return num.substr(n);
+}
+
+int main()
+{
+	string str = "765028321";
+	int k = 5;
+	cout << removeKdigits(str, k);
+	return 0;
+}