标签：style class blog code java http
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.
The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value.
The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.
If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed.
If no valid conversion could be performed, a zero value is returned. If the correct value is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned.
思路：题目不难，但是corner case比较多，需要仔细处理。
基本上都是自己处理的代码（未整理，有点乱。。）：
public class Solution {
public int atoi(String str) {
int max = 2147483647;
int min = -2147483648;
int result = 0;
int len = str.length();
int start = -1;
boolean neg = false;
for (int i = 0; i < len; i++) {
char ch = str.charAt(i);
if (ch == ‘+‘ || ch == ‘-‘ || (ch >= ‘0‘ && ch <= ‘9‘)) {
start = i;
break;
} else if (ch == ‘ ‘) {
} else {
break;
}
}
if (start == -1)
return 0;
if (str.charAt(start) == ‘-‘ || str.charAt(start) == ‘+‘) {
if (str.charAt(start) == ‘-‘)
neg = true;
start++;
}
for (int i = start; i < len; i++) {
char ch = str.charAt(i);
char next = 0;
if (i + 1 < len)
next = str.charAt(i + 1);
if (ch < ‘0‘ || ch > ‘9‘)
break;
result = 10 * result + (ch - ‘0‘);
if (next >= ‘0‘ && next <= ‘9‘) {
if (result > max / 10) {
if (neg)
return min;
else
return max;
}
if (result == max / 10) {
if (neg) {
if (next - ‘0‘ >= 8)
return min;
else
return -1 * (10 * result + (next - ‘0‘));
} else {
if (next - ‘0‘ >= 7)
return max;
else
return 10 * result + (next - ‘0‘);
}
}
}
}
if (neg)
result = -result;
return result;
}
public static void main(String[] args) {
System.out.println(new Solution().atoi(" -1010023630"));
System.out.println(new Solution().atoi(" -1010023630o4"));
System.out.println(new Solution().atoi(" 10522545459"));
System.out.println(new Solution().atoi(" 123"));
System.out.println(new Solution().atoi(" -123"));
System.out.println(new Solution().atoi(" +123"));
System.out.println(new Solution().atoi(" -1234bbsf3"));
System.out.println(new Solution().atoi(" 2147483646"));
System.out.println(new Solution().atoi(" 2147483647"));
System.out.println(new Solution().atoi(" 2147483648"));
System.out.println(new Solution().atoi(" 2147483649"));
System.out.println(new Solution()
.atoi(" 11111111111111111111111111111111111111111111111111"));
System.out.println(new Solution().atoi(" -2147483647"));
System.out.println(new Solution().atoi(" -2147483648"));
System.out.println(new Solution().atoi(" -2147483649"));
System.out.println(new Solution()
.atoi(" -11111111111111111111111111111111111111111111111111"));
System.out.println(new Solution().atoi("0"));
System.out.println(new Solution().atoi("abc"));
}
}
整理后，简单实现：
public class Solution {
public int atoi(String str) {
int max = Integer.MAX_VALUE;
int min = -Integer.MIN_VALUE;
long result = 0;
str = str.trim();
int len = str.length();
if (len < 1)
return 0;
int start = 0;
boolean neg = false;
if (str.charAt(start) == ‘-‘ || str.charAt(start) == ‘+‘) {
if (str.charAt(start) == ‘-‘)
neg = true;
start++;
}
for (int i = start; i < len; i++) {
char ch = str.charAt(i);
if (ch < ‘0‘ || ch > ‘9‘)
break;
result = 10 * result + (ch - ‘0‘);
if (!neg && result > max)
return max;
if (neg && -result < min)
return min;
}
if (neg)
result = -result;
return (int) result;
}
}
参考：
http://jane4532.blogspot.com/2013/09/string-to-integerleetcode.html
http://www.programcreek.com/2012/12/leetcode-string-to-integer-atoi/
[leetcode] [leetcode] String to Integer (atoi),布布扣,bubuko.com
[leetcode] [leetcode] String to Integer (atoi)
标签：style class blog code java http
原文地址：http://www.cnblogs.com/jdflyfly/p/3810677.html
