C++ program to Reorder the Given String to Form a K-Concatenated String

We are given a string and an integer k, and we need to reorder the characters in the string so that it becomes the concatenation of k similar substring. If not possible, output the result as "Impossible".

string = "malaalam";
K = 2;
res = solve(s, K);

Example (Using Maps)

Let's have a string "mottom" and K=2. The given string can be represented as the concatenation of 2 substrings like tomtom, motmot omtomt, etc. As in all 3, two substrings are joined together when k = 2.

Using the string, we can determine how many times each character occurs. After that, if all the available frequencies are divisible by k, then it is possible, and we can output any possible answer. Otherwise, it is not possible.

The C++ implementation of the above example is as follows ?

<div class="execute"></div><div class="code-mirror  language-cpp" contenteditable="plaintext-only" spellcheck="false" style="outline: none; overflow-wrap: break-word; overflow-y: auto; white-space: pre-wrap;"><span class="token macro property"><span class="token directive-hash">#</span><span class="token directive keyword">include</span> <span class="token string"><iostream></span></span>
<span class="token macro property"><span class="token directive-hash">#</span><span class="token directive keyword">include</span> <span class="token string"><map></span></span>
<span class="token keyword">using</span> <span class="token keyword">namespace</span> std<span class="token punctuation">;</span>
string <span class="token function">solve</span><span class="token punctuation">(</span>string s<span class="token punctuation">,</span> <span class="token keyword">int</span> k<span class="token punctuation">)</span> <span class="token punctuation">{</span>
   map<span class="token operator"><</span><span class="token keyword">char</span><span class="token punctuation">,</span> <span class="token keyword">int</span><span class="token operator">></span> mp<span class="token punctuation">;</span>
   <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">char</span> ch <span class="token operator">:</span> s<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      mp<span class="token punctuation">[</span>ch<span class="token punctuation">]</span><span class="token operator">++</span><span class="token punctuation">;</span>
   <span class="token punctuation">}</span>
   string repeatedSubstring <span class="token operator">=</span> <span class="token string">""</span><span class="token punctuation">;</span>
   <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">auto</span> <span class="token operator">&</span>val <span class="token operator">:</span> mp<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>val<span class="token punctuation">.</span>second <span class="token operator">%</span> k<span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
         <span class="token keyword">return</span> <span class="token string">"Impossible"</span><span class="token punctuation">;</span>
      <span class="token punctuation">}</span>
      <span class="token keyword">else</span> <span class="token punctuation">{</span>
         <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token operator">=</span><span class="token number">0</span><span class="token punctuation">;</span>i<span class="token operator"><</span>val<span class="token punctuation">.</span>second<span class="token operator">/</span>k<span class="token punctuation">;</span>i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            repeatedSubstring<span class="token operator">+=</span>val<span class="token punctuation">.</span>first<span class="token punctuation">;</span>
         <span class="token punctuation">}</span>
      <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
string ans <span class="token operator">=</span> <span class="token string">""</span><span class="token punctuation">;</span>
<span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> k<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
   ans<span class="token operator">+=</span> repeatedSubstring<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">return</span> ans<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">int</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
   string s <span class="token operator">=</span> <span class="token string">"mottom"</span><span class="token punctuation">;</span>
   <span class="token keyword">int</span> K <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>
   cout <span class="token operator"><<</span> <span class="token function">solve</span><span class="token punctuation">(</span>s<span class="token punctuation">,</span> K<span class="token punctuation">)</span><span class="token punctuation">;</span>
   <span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</div><div class="output-wrapper"><div class="console-close"></div><div class="code-output"></div></div>

Output

motmot

Example (Without Using Maps)

The C++ implementation of the same example, without using maps is as follows ?

<div class="execute"></div><div class="code-mirror  language-cpp" contenteditable="plaintext-only" spellcheck="false" style="outline: none; overflow-wrap: break-word; overflow-y: auto; white-space: pre-wrap;"><span class="token macro property"><span class="token directive-hash">#</span><span class="token directive keyword">include</span> <span class="token string"><bits/stdc++.h></span></span>
<span class="token keyword">using</span> <span class="token keyword">namespace</span> std<span class="token punctuation">;</span>

<span class="token keyword">int</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token punctuation">) </span><span class="token punctuation">{</span>
    string str <span class="token operator">=</span> <span class="token string">"mottom"</span><span class="token punctuation">;</span>
    <span class="token keyword">int</span> k <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>
    <span class="token keyword">int</span> frqncy<span class="token punctuation">[</span><span class="token number">26</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token punctuation">{</span> <span class="token number">0</span> <span class="token punctuation">}</span><span class="token punctuation">;</span>

    <span class="token keyword">int</span> len <span class="token operator">=</span> str<span class="token punctuation">.</span><span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> len<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        frqncy<span class="token punctuation">[</span>str<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">-</span> <span class="token string">'a'</span><span class="token punctuation">]</span><span class="token operator">++</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    string single_copy <span class="token operator">=</span> <span class="token string">""</span><span class="token punctuation">;</span>
    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> <span class="token number">26</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        <span class="token keyword">if</span> <span class="token punctuation">(</span>frqncy<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">!=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

            <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token punctuation">(</span>frqncy<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">%</span> k<span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token number">0</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>

                string ans <span class="token operator">=</span> <span class="token string">"Not Possible"</span><span class="token punctuation">;</span>
                cout <span class="token operator"><<</span> ans<span class="token punctuation">;</span>
            <span class="token punctuation">} </span><span class="token keyword">else</span> <span class="token punctuation">{</span>

                <span class="token keyword">int</span> total_occurrences <span class="token operator">=</span> <span class="token punctuation">(</span>frqncy<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">/</span> k<span class="token punctuation">)</span><span class="token punctuation">;</span>

                <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> j <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> j <span class="token operator"><</span> total_occurrences<span class="token punctuation">;</span> j<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
                    single_copy <span class="token operator">+=</span> <span class="token keyword">char</span><span class="token punctuation">(</span>i <span class="token operator">+</span> <span class="token number">97</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
                <span class="token punctuation">}</span>
            <span class="token punctuation">}</span>
        <span class="token punctuation">}</span>
    <span class="token punctuation">}</span>
    string kString<span class="token punctuation">;</span>
    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator"><</span> k<span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
        kString <span class="token operator">+=</span> single_copy<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    cout <span class="token operator"><<</span> kString<span class="token punctuation">;</span>
    <span class="token keyword">return</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</div><div class="output-wrapper"><div class="console-close"></div><div class="code-output"></div></div>

Output

motmot

Conclusion

We can use a map or unordered_map to hash the character to frequency. We can use an array of [26] for Latin lower case characters and set all freq to 0. This is an implementation-based problem with O(n) time complexity with unordered_map or hashmap.