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### by Sumit Chourasia | May 21, 2020 | Category :coding | Tags : leetcodealgorithmstringडेटा-संरचनाआसान

#### String Compression - मिनी टीवी

Given an array of characters, compress it in-place.

The length after compression must always be smaller than or equal to the original array.

Every element of the array should be a character (not int) of length 1.

After you are done modifying the input array in-place, return the new length of the array.

Could you solve it using only O(1) extra space?

Example 1:

``````Input:

["a","a","b","b","c","c","c"]

Output:

Return 6, and the first 6 characters of the input array should be: ["a","2","b","2","c","3"]

Explanation:

"aa" is replaced by "a2". "bb" is replaced by "b2". "ccc" is replaced by "c3".``````

Example 2:

``````Input:

["a"]

Output:

Return 1, and the first 1 characters of the input array should be: ["a"]

Explanation:

Nothing is replaced.``````

Example 3:

``````Input:

["a","b","b","b","b","b","b","b","b","b","b","b","b"]

Output:

Return 4, and the first 4 characters of the input array should be: ["a","b","1","2"].

Explanation:

Since the character "a" does not repeat, it is not compressed. "bbbbbbbbbbbb" is replaced by "b12".

Notice each digit has its own entry in the array.``````

Note:

``````All characters have an ASCII value in [35, 126].

1 <= len(chars) <= 1000.``````

Solution:

``````using System;
using System.Collections.Generic;
using System.Text;

{
public class CompressSoln
{
public int Compress(char[] chars)
{
if (chars==null)
return 0;
if (chars.Length == 1)
return 1;

int slow = 0;
int fast = 1;
int index = 0;
while(fast <= chars.Length)
{
if ( fast < chars.Length && chars[slow] == chars[fast])
{
fast++;
}
else if(fast == chars.Length)
{
slow = UpdateSlowFastPointer(chars, slow, fast,ref index);
break;
}
else
{
slow = UpdateSlowFastPointer(chars, slow, fast,ref index);
}
}

return index;
}

private static int UpdateSlowFastPointer(char[] chars, int slow, int fast,ref int index)
{
if (fast - slow == 1)
{
chars[index] = chars[slow];
if (chars.Length != fast)
{
slow++;
}
}
else
{
int diff = fast - slow;
var charArr = diff.ToString().ToCharArray();
chars[index] = chars[slow];
foreach (var item in charArr)
{
index++;
chars[index] = item;
}
slow=fast;
}
index++;

return slow;
}
}
}
``````

Time Complexity: O(n)

Space Complexity: O(1)

Test Cases:

``````using LeetCode.AskGif.Easy.String;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Text;

namespace CodingUnitTest.Easy.String
{
[TestClass]
public class CompressSolnTests
{
[TestMethod]
public void RepeatedSubstringPatternSoln_First()
{
var input = new char[] { 'a', 'a', 'b', 'b', 'c', 'c', 'c' };
var output = 6;
var res = new CompressSoln().Compress(input);

Assert.AreEqual(res, output);
}

[TestMethod]
public void RepeatedSubstringPatternSoln_Second()
{
var input = new char[] { 'a' };
var output = 1;
var res = new CompressSoln().Compress(input);

Assert.AreEqual(res, output);
}

[TestMethod]
public void RepeatedSubstringPatternSoln_Third()
{
var input = new char[] { 'a', 'b', 'b', 'b', 'b', 'b', 'b', 'b', 'b', 'b', 'b', 'b', 'b' };
var output = 4;
var res = new CompressSoln().Compress(input);

Assert.AreEqual(res, output);
}

[TestMethod]
public void RepeatedSubstringPatternSoln_Fourth()
{
var input = new char[] {'a', 'a', 'a', 'b', 'b', 'a', 'a'};
var output = 6;
var res = new CompressSoln().Compress(input);

Assert.AreEqual(res, output);
}

[TestMethod]
public void RepeatedSubstringPatternSoln_Fifth()
{
var input = new char[]{'a', 'a', 'a', 'a', 'a', 'b'};
var output = 3;
var res = new CompressSoln().Compress(input);

Assert.AreEqual(res, output);
}

[TestMethod]
public void RepeatedSubstringPatternSoln_Sixth()
{
var input = new char[] {'a', 'a', 'a', 'a', 'b', 'a'};
var output = 4;
var res = new CompressSoln().Compress(input);

Assert.AreEqual(res, output);
}
}
}
``````

Contributed By: Sumit Chourasia
Contributed By: Sumit Chourasia
Contributed By: Sumit Chourasia
Contributed By: Sumit Chourasia