Problem Description
Implement the function atoi. The function of the function is to convert a string to an integer.
Tip: Think carefully about all possible input situations. This question does not give input restrictions, you need to consider all possible situations yourself.
Input description:
input a string
Output description:
the integer of the output string
Example
Example 1
Enter
"123"
Output
123
Solutions
analysis
- Through the traversal method of adding and calculating, pay attention to the need to deal with signs and letters, as well as the number of out of bounds.
method
- Through the traversal method of adding and calculating, pay attention to the need to deal with signs and letters, as well as the number of out of bounds.
Code
// 思路1
public class Solution {
public int atoi(String str) {
// write code here
if (str == null || str.trim().length() < 1)
return 0;
//处理掉前后空格
char[] arr = str.trim().toCharArray();
int sign = 1, index = 0;
//判断正负号
if (arr[0] == '+')
index++;
if (arr[0] == '-') {
sign = -1;
index++;
}
int num = 0;
for (int i = index; i < arr.length; i++) {
if (arr[i] - '0' >= 0 && arr[i] - '9' <= 0) {
//如果当前运算会越界的时候，直接输出结果
if (num > Integer.MAX_VALUE / 10 || num == Integer.MAX_VALUE / 10 && arr[i] - '7' > 0) {
if (sign > 0)
return Integer.MAX_VALUE;
else
return Integer.MIN_VALUE;
}
num = 10 * num + arr[i] - '0';
} else
//如果是字母，跳出循环
break;
}
return num * sign;
}
}
Time complexity analysis:
O(N): Traverse the array
Space complexity analysis:
O(N): additional char array space
If you want to test, you can go directly to the link of Niuke.com to do the test