Performance of singles ifs Vs nested if

Hi, not able to wrap my head around why 2nd code snippet has better performance than the 1st.
This is C# code with reference to the problem.

https://leetcode.com/problems/find-all-anagrams-in-a-string/
Pasting the entire code below

			if(end - start + 1 == p.Length)  
            {
                if(count == 0)
                    output.Add(start); 
                
                if(map[s[start] - 'a']++ >= 0)
                    count++;
                
                start++;
            }

			if(count == 0)
            {                  
                output.Add(start);                 
            }             
           
            if(end - start + 1 == p.Length && map[s[start++] - 'a']++ >= 0)           
                count++;

Complete code:

 public IList<int> FindAnagrams(string s, string p) {
        
        List<int> output = new List<int>();
        if(s == null || s.Length == 0)
            return output;
        
        int[] map = new int[26];
        foreach(char c in p.ToCharArray())
        {
            map[c - 'a']++;
        }
        
        int count = p.Length;
        int start = 0;
        int end;
        for(end = 0; end < s.Length; end++)
        {            
            if(map[s[end] - 'a']-- > 0)
            { 
                count--;
            }
            
            if(count == 0)
            {                  
                output.Add(start);                 
            }             
           
            if(end - start + 1 == p.Length && map[s[start++] - 'a']++ >= 0)           
                count++;
            
        }
        return output;
    }
}

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