Subject description:
https://leetcode-cn.com/problems/ba-zi-fu-chuan-zhuan-huan-cheng-zheng-shu-lcof/
Write a function StrToInt, to achieve this function converts the string to an integer. You can not use atoi or other similar library functions.
First, the function will begin with a space character discard useless if necessary, until the find to the first non-space character so far.
When we find the first non-space character is a positive or negative number, the combination of the symbols as much as possible with consecutive numbers up later, as the sign of integer; if the first non-space character is figures, which directly after the continuous numeric characters are combined to form an integer.
In addition to the string after a valid integer part may also exist extra characters, these characters can be ignored, they should not affect a function.
Note: if the character string in the first non-space character is not a valid integer character string is empty or contains only white space character string, then you will not need to be a function of conversion.
In any case, if the function can not effectively convert, 0 is returned.
Description:
We assume that the environment can store 32-bit signed integer size, then the numerical range [-231 231--1]. If the value exceeds this range, return INT_MAX (231 - 1) or INT_MIN (-231).
Example 1:
Input: "42"
Output: 42
Example 2:
Input: "-42"
Output: -42
Explanation: a first non-blank character '-', it is a negative sign.
We will all digital consecutive negative number and later combined as much as possible, and finally get -42.
Example 3:
Input: "4193 with words"
Output: 4193
Explanation: converting the digital OFF '3', because the next character is not numeric.
Example 4:
Input: "words and 987"
Output: 0
Explanation: a first non-blank character 'w', but it is not a positive number or negative number.
Therefore, the conversion can not be performed effectively.
Example 5:
Input: "-91283472332"
Output: -2147483648
explanation: the number "-91283472332" Over the range of 32-bit signed integer.
So return INT_MIN (-231).
Topic analysis:
Not analysis, and problem-solving ideas very clear, however, is to deal with boundary conditions need to be considered comprehensive, the reason for writing this question, because I was wrong many times. . .
Java code:
public int strToInt(String str) { long result = 0; if (str == null || str.isEmpty()) { return (int) result; } // 去除空格 str = str.trim(); if (str.isEmpty() || !(str.startsWith("+") || str.startsWith("-") || Character.isDigit(str.charAt(0)))) { return (int) result; } boolean isNeg = str.startsWith ( "-" ); // find the first digit of the index is not int startIndex = isNeg || str.startsWith ( "+") 1:? 0 ; int index = startIndex; the while (index <str.length () && by Character.isDigit (str.charAt (index))) { index++; } // 截取字符串 str = str.substring(startIndex, index); int powIndex = 0; for (int i = str.length() - 1; i >= 0; i--) { if (!Character.isDigit(str.charAt(i))) { break; } result += Math.pow(10, powIndex++) * (str.charAt(i) - '0'); if (isNeg && (-result) <= Integer.MIN_VALUE) { return Integer.MIN_VALUE; } if (!isNeg && result >= Integer.MAX_VALUE) { return Integer.MAX_VALUE; } } return isNeg ? (int) (-result) : (int) result; }
Power button and submit the results of running times:
To see how ill-considered. . .
