leetcode_rust/problems/p000_0xx/
p000_009.rs

1//! # Description
2//!
3//! Given an integer `x`, return `true` if `x` is a
4//! palindrome, and `false` otherwise.
5//!
6//! Example 1:
7//!
8//! ```plain
9//! Input: x = 121
10//! Output: true
11//! Explanation: 121 reads as 121 from left to right and from right to left.
12//! ```
13//!
14//! Example 2:
15//!
16//! ```plain
17//! Input: x = -121
18//! Output: false
19//! Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.
20//! ```
21//!
22//! Example 3:
23//!
24//! ```plain
25//! Input: x = 10
26//! Output: false
27//! Explanation: Reads 01 from right to left. Therefore it is not a palindrome.
28//! ```
29//!  
30//! Constraints:
31//!
32//! $-2^{31} \leqslant x \leqslant 2^{31} - 1$
33//!  
34//! Follow up: Could you solve it without converting the integer to a string?
35//!
36//! Source: <https://leetcode.com/problems/palindrome-number/>
37
38////////////////////////////////////////////////////////////////////////////////
39
40/// Check if a given input is a palindrome number
41///
42/// # Arguments
43/// * `x` - input number
44///
45/// # Examples
46/// ```
47/// use leetcode_rust::problems::p000_0xx::p000_009::is_palindrome;
48///
49/// assert!(is_palindrome(12321) == true);
50/// assert!(is_palindrome(-12321) == false);
51/// ```
52pub fn is_palindrome(number: i32) -> bool {
53    // alg_1(number)
54    alg_2(number)
55}
56
57/// Algorithm 1: check digits using double-sided queue.
58///
59/// # Arguments
60/// * `number` - input number to check
61#[allow(dead_code)]
62fn alg_1(mut number: i32) -> bool {
63    if number < 0 {
64        return false;
65    }
66    let mut temp: Vec<i32> = vec![];
67
68    while number >= 10 {
69        temp.push(number % 10);
70        if number >= 10 {
71            number = number / 10;
72        }
73    }
74    temp.push(number);
75
76    if temp.len() == 2 {
77        return temp[0] == temp[1];
78    }
79
80    let mut idx_start = 0;
81    let mut idx_end = temp.len() - 1;
82
83    loop {
84        if idx_end == idx_start {
85            return true;
86        }
87
88        if idx_end - idx_start == 1 {
89            return temp[idx_end] == temp[idx_start];
90        }
91
92        if temp[idx_end] != temp[idx_start] {
93            return false;
94        }
95        idx_end -= 1;
96        idx_start += 1;
97    }
98}
99
100/// Algorithm 2: check digits fast subtraction.
101///
102/// # Arguments
103/// * `number` - input number to check
104#[allow(dead_code)]
105fn alg_2(mut number: i32) -> bool {
106    if number < 0 {
107        return false;
108    }
109
110    // One digit shorter than actual length.
111    let mut digits = (number as f32).log10().floor() as usize;
112    if digits == 0 {
113        return true;
114    }
115
116    loop {
117        number = (number - (number % 10) * 10i32.pow(digits as u32)) / 10;
118        if number < 0 || digits <= 1 {
119            break;
120        }
121
122        digits -= 2;
123    }
124
125    number == 0
126}
leetcode_rust/problems/p000_0xx/p000_009.rs

leetcode_rust/problems/p000_0xx/
p000_009.rs
