<p>Given a positive integer <code>n</code>, find <em>the smallest integer which has exactly the same digits existing in the integer</em> <code>n</code> <em>and is greater in value than</em> <code>n</code>. If no such positive integer exists, return <code>-1</code>.</p>

<p><strong>Note</strong> that the returned integer should fit in <strong>32-bit integer</strong>, if there is a valid answer but it does not fit in <strong>32-bit integer</strong>, return <code>-1</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> n = 12
<strong>Output:</strong> 21
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> n = 21
<strong>Output:</strong> -1
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 2<sup>31</sup> - 1</code></li>
</ul>

class Solution {
public:
    int nextGreaterElement(int n) {
        string s=to_string(n);
        int flag=0,n1=s.size(),ind=-1,x=n1;
        stack<int> st;
        for(int i=n1-1;i>=0;i--){
            while(!st.empty()&&s[st.top()]>s[i]){
                flag=1;
                ind=st.top();
                st.pop();
            }
            if(flag){
                swap(s[i],s[ind]);
                x=i+1;
                break;
            }
            st.push(i);
        }
        sort(s.begin()+x,s.end());
        long long no=stoll(s);
        if(no==n||no>INT_MAX)
        return -1;
        return no;
    }
};
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