Kindergarten adventure - study code D - score 30 (maximum score 30)

kindergartenAdventure_studycodeD.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
class Solution {
    
    static void D(Dictionary<int,int> d) {
        Console.WriteLine("---");
        foreach (var k in d.Keys) {
            Console.WriteLine("\t" + k + ":\t" + d[k]);
        }
        Console.WriteLine("---");
    }
    static void Main(String[] args) {
        int n = int.Parse(Console.ReadLine());
        var arr = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
        var d = new Dictionary<int, int>();
        int willMakeIt = 0;
        for (int i = 0; i < arr.Length; i++) {
            int timeLeft = i - arr[i];
            if (!d.ContainsKey(timeLeft)) d[timeLeft] = 0;
            d[timeLeft]++;
            if (timeLeft >= 0) willMakeIt++;
        }
        //D(d);
        //Console.WriteLine(string.Format("{0}: {1}", 0, willMakeIt));
        
        int best = willMakeIt;
        int bestIndex = 0;
        for (int i = 1; i < arr.Length; i++) {
            int originalTimeLeftForPrevious = i - 1 - arr[i-1];
            d[originalTimeLeftForPrevious]--;
            
            if (d.ContainsKey(i-1)) {
                willMakeIt -= d[i-1];
            }
            
            int newTimeLeftForPrevious = n - 1 - arr[i-1] + i;
            if (!d.ContainsKey(newTimeLeftForPrevious)) d[newTimeLeftForPrevious] = 0;
            d[newTimeLeftForPrevious]++;
            if (newTimeLeftForPrevious - i >= 0 && originalTimeLeftForPrevious < i-1) willMakeIt++;
            
            //D(d);
            //Console.WriteLine(string.Format("{0}: {1}", i, willMakeIt));
            
            if (willMakeIt > best) { best = willMakeIt; bestIndex = i; }
        }
        Console.WriteLine(bestIndex + 1);
    }
}