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.
Update (2015-02-10):
The signature of the C++ function had been updated. If you still see your function signature accepts a const char * argument, please click the reload button to reset your code definition.
答案
在判断数字是否越界的时候,若假设int数字范围是[-128,127],对于数字130,当读到13时,13 > 127/10,因此第一个判定条件是result > Integer.MAX_VALUE / 10;对于数字128,当读到12时,8 > 127 % 10,因此第二个判定条件是tail > Integer.MAX_VALUE % 10。1
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30 public static int myAtoi(String str) {
if ("".equals(str)) return 0;
char[] c = str.toCharArray();
int len = c.length;
int i = 0;
int sign = 1;
while (c[i] == ' ') i++;
if (c[i] == '-') {
sign = -1;
i++;
} else if (c[i] == '+') i++;
int result = 0;
while (i < len) {
if (c[i] < '0' || c[i] > '9') break;
int tail = c[i] - '0';
if (sign == 1) {
if (result > Integer.MAX_VALUE / 10
|| result == Integer.MAX_VALUE / 10 && tail > Integer.MAX_VALUE % 10)
return sign * Integer.MAX_VALUE;
} else {
if (result > Integer.MAX_VALUE / 10 || result == Integer.MAX_VALUE / 10 && tail > Integer.MIN_VALUE % 10 + 1)
return Integer.MIN_VALUE;
}
result = result * 10 + tail;
i++;
}
return sign * result;
}