LeetCode 8 – String to Integer atoi

public int atoi(String str) {
  char[] C = str.toCharArray();
  int N = C.length;
  int i = 0;
  int neg = 1;
  while(i < N && C[i] == ' ') i++; // we are at first nonspace char
  if(i == N) return 0; // out of characters

  if(C[i] == '+') i++;
  else if(C[i] == '-'){
    neg = -1;
    i++;
  }
  if(i == N) return 0; // out of chars

  if(C[i] < '0' && C[i] > '9') return 0; // wrong first character

  // C[i] is now the beginning of the number

  int result = 0;

  // Check for overflows and return the appropriate limit
  while(i < N && C[i] <= '9' && C[i] >= '0'){
    int digit = C[i] - '0';
    if(result > Integer.MAX_VALUE/10) return (neg > 0) ? Integer.MAX_VALUE : Integer.MIN_VALUE;
    result = 10*result;
    if(result > Integer.MAX_VALUE-digit) return (neg > 0) ? Integer.MAX_VALUE : Integer.MIN_VALUE;
    result += digit;
    i++;
  }

  return neg*result;
}