#include <string>
#include <iostream>
#include <cctype>

/**
 * 8. String to Integer
 * Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer (similar to C/C++'s atoi function).
 * The algorithm for myAtoi(string s) is as follows:
 * Read in and ignore any leading whitespace.
 * Check if the next character (if not already at the end of the string) is '-' or '+'. Read this character in if it is either. This determines if the final result is negative or positive respectively. Assume the result is positive if neither is present.
 * Read in next the characters until the next non-digit character or the end of the input is reached. The rest of the string is ignored.
 * Convert these digits into an integer (i.e. "123" -> 123, "0032" -> 32). If no digits were read, then the integer is 0. Change the sign as necessary (from step 2).
 * If the integer is out of the 32-bit signed integer range [-231, 231 - 1], then clamp the integer so that it remains in the range. Specifically, integers less than -231 should be clamped to -231, and integers greater than 231 - 1 should be clamped to 231 - 1.
 * Return the integer as the final result.
 * Note:
 * Only the space character ' ' is considered a whitespace character.
 * Do not ignore any characters other than the leading whitespace or the rest of the string after the digits.
 */

class Solution {
public:
	static int myAtoi(const std::string& s) {
		long long ret = 0;
		int sgn = 1, pos = 0;
		for (; std::isspace(s[pos]); ++pos);
		if (s[pos] == '-')
			sgn = -sgn;
		if (s[pos] == '-' || s[pos] == '+')
			++pos;
		for (; std::isdigit(s[pos]); ++pos) {
			ret = (ret << 3) + (ret << 1) + (s[pos] ^ 48);
			if (ret > INT32_MAX)
				break;
		}
		ret *= sgn;
		if (ret < INT32_MIN)
			return INT32_MIN;
		else if (ret > INT32_MAX)
			return INT32_MAX;
		return int(ret & 0xFFFFFFFFLL);
	}
};

int main() {
	std::cout << Solution::myAtoi("42");
	return 0;
}