8. String to Integer (atoi) Medium
1/**
2 * [8] String to Integer (atoi)
3 *
4 * Implement the myAtoi(string s) function, which converts a string to a 32-bit signed integer
5 * (similar to C/C++'s atoi function).
6 * The algorithm for myAtoi(string s) is as follows:
7 * <ol>
8 * Read in and ignore any leading whitespace.
9 * Check if the next character (if not already at the end of the string) is '-' or '+'.
10 * Read this character in if it is either. This determines if the final result is negative
11 * or positive respectively. Assume the result is positive if neither is present.
12 * Read in next the characters until the next non-digit charcter or the end of the input
13 * is reached. The rest of the string is ignored.
14 * Convert these digits into an integer (i.e. "123" -> 123, "0032" -> 32). If no digits
15 * were read, then the integer is 0. Change the sign as necessary (from step 2).
16 * If the integer is out of the 32-bit signed integer range [-2^31, 2^31 - 1], then
17 * clamp the integer so that it remains in the range. Specifically, integers less
18 * than -2^31 should be clamped to -2^31, and integers greater than 2^31 - 1 should be clamped to 2^31 - 1.
19 * Return the integer as the final result.
20 * </ol>
21 * Note:
22 *
23 * Only the space character ' ' is considered a whitespace character.
24 * Do not ignore any characters other than the leading whitespace or the rest of
25 * the string after the digits.
26 *
27 *
28 * Example 1:
29 *
30 * Input: s = "42"
31 * Output: 42
32 * Explanation: The underlined characters are what is read in, the caret is the
33 * current reader position.
34 * Step 1: "42" (no characters read because there is no leading whitespace)
35 * ^
36 * Step 2: "42" (no characters read because there is neither a '-' nor '+')
37 * ^
38 * Step 3: "<u>42</u>" ("42" is read in)
39 * ^
40 * The parsed integer is 42.
41 * Since 42 is in the range [-2^31, 2^31 - 1], the final result is 42.
42 *
43 * Example 2:
44 *
45 * Input: s = " -42"
46 * Output: -42
47 * Explanation:
48 * Step 1: "<u> </u>-42" (leading whitespace is read and ignored)
49 * ^
50 * Step 2: " <u>-</u>42" ('-' is read, so the result should be negative)
51 * ^
52 * Step 3: " -<u>42</u>" ("42" is read in)
53 * ^
54 * The parsed integer is -42.
55 * Since -42 is in the range [-2^31, 2^31 - 1], the final result is -42.
56 *
57 * Example 3:
58 *
59 * Input: s = "4193 with words"
60 * Output: 4193
61 * Explanation:
62 * Step 1: "4193 with words" (no characters read because there is no leading whitespace)
63 * ^
64 * Step 2: "4193 with words" (no characters read because there is neither a '-' nor '+')
65 * ^
66 * Step 3: "<u>4193</u> with words" ("4193" is read in; reading stops because the next character is a non-digit)
67 * ^
68 * The parsed integer is 4193.
69 * Since 4193 is in the range [-2^31, 2^31 - 1], the final result is 4193.
70 *
71 * Example 4:
72 *
73 * Input: s = "words and 987"
74 * Output: 0
75 * Explanation:
76 * Step 1: "words and 987" (no characters read because there is no leading whitespace)
77 * ^
78 * Step 2: "words and 987" (no characters read because there is neither a '-' nor '+')
79 * ^
80 * Step 3: "words and 987" (reading stops immediately because there is a non-digit 'w')
81 * ^
82 * The parsed integer is 0 because no digits were read.
83 * Since 0 is in the range [-2^31, 2^31 - 1], the final result is 0.
84 *
85 * Example 5:
86 *
87 * Input: s = "-91283472332"
88 * Output: -2147483648
89 * Explanation:
90 * Step 1: "-91283472332" (no characters read because there is no leading whitespace)
91 * ^
92 * Step 2: "<u>-</u>91283472332" ('-' is read, so the result should be negative)
93 * ^
94 * Step 3: "-<u>91283472332</u>" ("91283472332" is read in)
95 * ^
96 * The parsed integer is -91283472332.
97 * Since -91283472332 is less than the lower bound of the range [-2^31, 2^31 - 1], the
98 * final result is clamped to -2^31 = -2147483648.<span style="display: none;"> </span>
99 *
100 *
101 * Constraints:
102 *
103 * 0 <= s.length <= 200
104 * s consists of English letters (lower-case and upper-case), digits (0-9), ' ', '+', '-', and '.'.
105 *
106 */
107pub struct Solution {}
108
109// problem: https://leetcode.com/problems/string-to-integer-atoi/
110// discuss: https://leetcode.com/problems/string-to-integer-atoi/discuss/?currentPage=1&orderBy=most_votes&query=
111
112// submission codes start here
113
114impl Solution {
115 pub fn my_atoi(s: String) -> i32 {
116 let chs: Vec<char> = s.chars().collect();
117 let mut i = 0;
118 let mut negative = false;
119 let mut result: i64 = 0;
120
121 while i < chs.len() {
122 if chs[i] == ' ' {
123 i += 1;
124 continue;
125 }
126
127 if chs[i] == '-' {
128 negative = true;
129 i += 1;
130 break;
131 } else if chs[i] == '+' {
132 negative = false;
133 i += 1;
134 break;
135 }
136
137 if !chs[i].is_numeric() {
138 return 0;
139 } else {
140 break
141 }
142 }
143
144 while i < chs.len() {
145 if chs[i].is_numeric() {
146 result = result * 10 + chs[i] as i64 - '0' as i64;
147 if !negative && result > i32::MAX as i64 {
148 return i32::MAX;
149 } else if negative && -result < i32::MIN as i64 {
150 return i32::MIN;
151 }
152 i += 1;
153 } else {
154 break;
155 }
156 }
157
158 if negative {
159 result = -result;
160 }
161
162 if result > i32::MAX as i64 {
163 i32::MAX
164 } else if result < i32::MIN as i64 {
165 i32::MIN
166 } else {
167 result as i32
168 }
169 }
170}
171
172// submission codes end
173
174#[cfg(test)]
175mod tests {
176 use super::*;
177
178 #[test]
179 fn test_8() {
180 assert_eq!(Solution::my_atoi("12344".to_string()), 12344);
181 assert_eq!(Solution::my_atoi(" -12344".to_string()), -12344);
182 assert_eq!(Solution::my_atoi(" s +12344".to_string()), 0);
183 assert_eq!(Solution::my_atoi(" +12344".to_string()), 12344);
184 assert_eq!(Solution::my_atoi(" +12344s3".to_string()), 12344);
185 assert_eq!(Solution::my_atoi(" +-112344s3".to_string()), 0);
186 assert_eq!(Solution::my_atoi("9223372036854775808".to_string()), i32::MAX);
187 assert_eq!(Solution::my_atoi("-9223372036854775808".to_string()), i32::MIN);
188 assert_eq!(Solution::my_atoi((i32::MAX as i64 + 11).to_string()), i32::MAX);
189 }
190}
191Back
© 2025 bowen.ge All Rights Reserved.