P008 String to Integer (atoi)

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

思路分析

关键是注意特殊情况的处理:

  • 输入空字符==>0
  • 对输入进行trim
  • 注意可能出现的正号(+)和负号(-)
  • 读取到非字符时停止，并将前面的结果返回
  • 注意溢出问题==> Integer.MAX_VALUE 或者 Integer.MIN_VALUE

代码

java

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public class Solution008 {
	public int myAtoi(String str) {
		if (str == null)
			return 0;
		str = str.trim();
		if ("".equals(str))
			return 0;
		StringBuilder sb = new StringBuilder();
		int sign = 1;
		if (str.startsWith("+")) {
			str = str.replaceFirst("\\+", "");
		} else if (str.startsWith("-")) {
			sign = -1;
			str = str.replaceFirst("-", "");
		}
		for (int i = 0; i < str.length(); i++) {
			char c = str.charAt(i);
			if (c > '9' || c < '0') {
				break;
			}
			sb.append(c);
		}
		try {
			long l = sign * Long.parseLong(sb.toString());
			if (l >= Integer.MAX_VALUE)
				return Integer.MAX_VALUE;
			if (l <= Integer.MIN_VALUE)
				return Integer.MIN_VALUE;
			return (int) (l);
		} catch (Exception e) {
			// e.printStackTrace();
			return 0;
		}
	}
	public static void main(String[] args) {
		System.out.println(Integer.MIN_VALUE);
		System.out.println(Integer.MAX_VALUE);
		Solution008 s8 = new Solution008();
		String strs[] = { //
				"", "-2147483648", "-2147483649", "2147483648", "-2147483648", //
				"1010023630", "-1010023630", //
				"   10522545459", " 10522545459+123 ", //
				"-123", "+123", " -123 ", "+123sdf", //
				"11111111111111111111111111111111111111111111111111", //
				"sfjdk", "-fjdks", "+fjsdk" };
		for (String s : strs) {
			System.out.println(s + "-->" + s8.myAtoi(s));
		}
	}
}

python

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class Solution008(object):
    def myAtoi(self, s):
        """
        :type str: str
        :rtype: int
        """
        
        if not s:return 0
        s = s.strip()
        
        if "" == s:return 0
        sign = 1;strs = "0"
        
        if s[0] == "+":
            s = s[1:]
        elif s[0] == "-":
            sign = -1
            s = s[1:]
        
        for c in s:
            if c > '9' or c < '0':
                break
            strs += c
        
        l = long(strs) * sign
        
        if l <= -2147483648:return - 2147483648
        if l >= 2147483647:return 2147483647
        
        return (int)(l)