1. 题目
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.
2. 思路
功能相对简单,但是题目描述和最有的判定要求太模糊。
比如标准答案不考虑8进制和16进制的数字字面形式的处理。
对于前导0进行持续忽略处理。
注意1:符号位+-
注意2:越界的字面返回最大值或者最小值
注意3:021不是8进制的17,而是十进制的21.
注意4:0x12不是16进制的18,而是0.
3. 代码
耗时:16ms
class Solution {
public:
int myAtoi(string str) {
int len = str.length();
if (len == 0) return 0;
long long r = 0;
int flag = 1;
int i = 0;
while (str[i] == ' ') {
i++;
}
if (str[i]=='-') {
flag = -1;
i++;
} else if (str[i]=='+'){
i++;
}
for (; i < len; i++) {
char ch = str[i];
if (ch >= '0' && ch <= '9') {
r = r * 10 + ch - '0';
} else {
break;
}
if (r > numeric_limits<int>::max()) break;
}
if ((flag == 1 && r > numeric_limits<int>::max())
|| (flag == -1 && -r < numeric_limits<int>::min())) {
return flag == 1 ? numeric_limits<int>::max() : numeric_limits<int>::min();
} else {
return r * flag;
}
}
int myAtoi_backup(string str) {
if (str.length() == 0) return 0;
long long r = 0;
int flag = 1;
int i = 0;
if (str[0] == '-') {
flag = -1;
i++;
} else if (str[0] == '+') {
i++;
}
int base = 10;
if (str[i] == '0' && i+1 < str.length() && (str[i+1] == 'x' || str[i+1] == 'X')) {
base = 16;
i += 2;
} else if (str[i] == '0') {
base = 8;
i++;
}
for (; i < str.length(); i++) {
char ch = str[i];
if ((base == 10 && ch >= '0' && ch <= '9')
|| (base == 8 && ch >= '0' && ch <= '7')
|| (base == 16 && (ch >= '0' && ch <= '9' || ch >= 'a' && ch <= 'f' || ch >= 'A' && ch <= 'F'))) {
r = r * base;
int delta = ch - '0';
if (base == 16) {
delta = 10;
if (ch >= 'a' && ch <= 'f') {
delta += ch - 'a';
} else if (ch >= 'A' && ch <= 'F') {
delta += ch - 'A';
}
}
r += delta;
if (r > numeric_limits<int>::max()) {
return 0;
}
} else {
return r * flag;
}
}
return r * flag;
}
};
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