8. String to Integer (atoi)
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description:
String to Integer (atoi)
14.0%MediumImplement 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.
spoilers alert... click to show requirements for atoi.
my solution:
int myAtoi(char* str) { long long sum = 0; bool flag = true; bool track = true; bool track2 = true; for (int i = 0; str[i] != '\0'; i++) { if ((str[i] == '+' || str[i] == '-') && track) { track = false; track2 = false; if (str[i] == '-') flag = false; continue; } else if (str[i] == '+' || str[i] == '-') return 0; if (str[i] >= '0' && str[i] <= '9' && flag) { sum += str[i] - '0'; if (sum > 2147483647) { return 2147483647; } track2 = false; } else if (str[i] >= '0' && str[i] <= '9' && !flag) { sum -= str[i] - '0'; if (sum < -2147483648) { return -2147483648; } track2 = false; } else if (str[i] == ' ' && track2) continue; else return sum; if (str[i + 1] != '\0' && str[i + 1] >= '0' && str[i +1] <= '9') sum *= 10; } return sum;}better ways:
by yuruofeifei
int atoi(const char *str) { int sign = 1, base = 0, i = 0; while (str[i] == ' ') { i++; } if (str[i] == '-' || str[i] == '+') { sign = 1 - 2 * (str[i++] == '-'); } while (str[i] >= '0' && str[i] <= '9') { if (base > INT_MAX / 10 || (base == INT_MAX / 10 && str[i] - '0' > 7)) { if (sign == 1) return INT_MAX; else return INT_MIN; } base = 10 * base + (str[i++] - '0'); } return base * sign;}
thought:
注意溢出的范围,学习了一个快速把字符串转化成整形的方法。
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- 8.String to Integer (atoi)
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- 8. String to Integer (atoi)
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- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
- 8. String to Integer (atoi)
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