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  1. Prepare
  2. Algorithms
  3. Warmup
  4. Diagonal Difference
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Diagonal Difference

  • bogdanh
     + 1 comment

    This is a solution where we go through the matrix only once, no arrays just check if we add the number to one of the diagonals or both.

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        
        int N = in.nextInt();
        int sumA =0, sumB = 0;
        int M = N*N;
        //counter for first diagonal
        int countA = N-N;  // 0   -> N*N  ; step N+1  
        // counte for second diagonal
        int countB = N-1;  // N-1 -> N*N-N; step N-1 
        int countBLimit = M-1; // the last element is not for this diagonal 
        
        for (int i = 0; i<M; i++) {
            int k = in.nextInt();

            if (i == countA) { 
                sumA += k;
                countA += N+1;
            }
            
            if (i == countB && countB < countBLimit) {
               sumB += k;
               countB += N-1;
            }
        }
        System.out.println(Math.abs(sumA-sumB)); 
    }