LeetCode 008 String to Integer (atoi)

本文介绍了一个atoi函数的实现,该函数用于将字符串转换为整数。解析了如何处理字符串前后的空白字符,识别正负号,以及如何在遇到非数字字符时停止转换。同时,讨论了如何处理超出32位整数范围的情况。

String to Integer (atoi)

Implement atoi which converts a string to an integer.

The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value.

The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.

If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed.

If no valid conversion could be performed, a zero value is returned.

Note:

  • Only the space character ’ ’ is considered as whitespace character.
  • Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231, 231 − 1]. If the numerical value is out of the range of representable values, INT_MAX (231 − 1) or INT_MIN (−231) is returned.

Example 1:

Input: “42”
Output: 42

Example 2:

Input: " -42"
Output: -42
Explanation: The first non-whitespace character is ‘-’, which is the minus sign. Then take as many numerical digits as possible, which gets 42.

Example 3:

Input: “4193 with words”
Output: 4193
Explanation: Conversion stops at digit ‘3’ as the next character is not a numerical digit.

Example 4:

Input: “words and 987”
Output: 0
Explanation: The first non-whitespace character is ‘w’, which is not a numerical digit or a +/- sign. Therefore no valid conversion could be performed.

Example 5:

Input: “-91283472332”
Output: -2147483648
Explanation: The number “-91283472332” is out of the range of a 32-bit signed integer. Thefore INT_MIN (−231) is returned.

题目分析

将字符串转为int
有几点需要注意的是:

  • 字符串前后可能存在空格,应该先丢弃空白字符,找到第一个非空白字符。
  • 然后判断符号,复数有负号。输出时也要输出负号。
  • 若是第一个非空字符不是符号也不是数字,那么直接返回0。
  • 若是超过了int型的上限或者是下限。则输出int型的上下限值。-2147483648 或 2147483647。

代码实在是忍不住用用了网上大神写的,思路太好了,没忍住就抬出来壮壮门面了。好像现在都是贴的人家的程序。咦。这个要注意了以后。

class Solution {
		public int myAtoi(String str) {
			String strTrim = str.trim(); // remove any leading and trailing whitespace
			if (strTrim.length() == 0)
				return 0;
			int index = 0, sign = 1;
			long result = 0;//设置为long型,否则超过上下限就会跳变。无法作比较。
			if (strTrim.charAt(index) == '+' || strTrim.charAt(index) == '-') {
				sign = strTrim.charAt(index) == '+' ? 1 : -1; // get the sign of the number
				index++;
			}
			// convert string to integer without overflow
			while (index < strTrim.length()) {
				int digit = strTrim.charAt(index) - '0'; // get the first digit
				if (digit < 0 || digit > 9)//当出现了非数字字符,则可以停止了
					break;
				result = result * 10 + digit; // add the digit to result
				if (result > Integer.MAX_VALUE) { // detect the overflow
					return sign == 1 ? Integer.MAX_VALUE : Integer.MIN_VALUE;
				}
				index++;
			}
			return (int) (result * sign);
		}
	}
内容概要:本文系统介绍了算术优化算法(AOA)的基本原理、核心思想及Python实现方法,并通过图像分割的实际案例展示了其应用价值。AOA是一种基于种群的元启发式算法,其核心思想来源于四则运算,利用乘除运算进行全局勘探,加减运算进行局部开发,通过数学优化器加速函数(MOA)和数学优化概率(MOP)动态控制搜索过程,在全局探索与局部开发之间实现平衡。文章详细解析了算法的初始化、勘探与开发阶段的更新策略,并提供了完整的Python代码实现,结合Rastrigin函数进行测试验证。进一步地,以Flask框架搭建前后端分离系统,将AOA应用于图像分割任务,展示了其在实际工程中的可行性与高效性。最后,通过收敛速度、寻优精度等指标评估算法性能,并提出自适应参数调整、模型优化和并行计算等改进策略。; 适合人群:具备一定Python编程基础和优化算法基础知识的高校学生、科研人员及工程技术人员,尤其适合从事人工智能、图像处理、智能优化等领域的从业者;; 使用场景及目标:①理解元启发式算法的设计思想与实现机制;②掌握AOA在函数优化、图像分割等实际问题中的建模与求解方法;③学习如何将优化算法集成到Web系统中实现工程化应用;④为算法性能评估与改进提供实践参考; 阅读建议:建议读者结合代码逐行调试,深入理解算法流程中MOA与MOP的作用机制,尝试在不同测试函数上运行算法以观察性能差异,并可进一步扩展图像分割模块,引入更复杂的预处理或后处理技术以提升分割效果。
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