From 6d9f5a16bf6aa8e700b3b518852b50da92db5029 Mon Sep 17 00:00:00 2001
From: EFanZh <efanzh@gmail.com>
Date: Thu, 2 May 2024 15:54:01 +0800
Subject: [PATCH] Add problem 1849: Splitting a String Into Descending
 Consecutive Values

---
 src/lib.rs                                    |  1 +
 .../backtracking.rs                           | 86 +++++++++++++++++++
 .../mod.rs                                    | 26 ++++++
 3 files changed, 113 insertions(+)
 create mode 100644 src/problem_1849_splitting_a_string_into_descending_consecutive_values/backtracking.rs
 create mode 100644 src/problem_1849_splitting_a_string_into_descending_consecutive_values/mod.rs

diff --git a/src/lib.rs b/src/lib.rs
index c818c32a..725d24e5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1377,6 +1377,7 @@ pub mod problem_1844_replace_all_digits_with_characters;
 pub mod problem_1845_seat_reservation_manager;
 pub mod problem_1846_maximum_element_after_decreasing_and_rearranging;
 pub mod problem_1848_minimum_distance_to_the_target_element;
+pub mod problem_1849_splitting_a_string_into_descending_consecutive_values;
 pub mod problem_1851_minimum_interval_to_include_each_query;
 pub mod problem_1854_maximum_population_year;
 pub mod problem_1855_maximum_distance_between_a_pair_of_values;
diff --git a/src/problem_1849_splitting_a_string_into_descending_consecutive_values/backtracking.rs b/src/problem_1849_splitting_a_string_into_descending_consecutive_values/backtracking.rs
new file mode 100644
index 00000000..ffc95c03
--- /dev/null
+++ b/src/problem_1849_splitting_a_string_into_descending_consecutive_values/backtracking.rs
@@ -0,0 +1,86 @@
+pub struct Solution;
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+use std::cmp::Ordering;
+use std::str::Bytes;
+
+impl Solution {
+    fn check(mut first: u8, mut iter: Bytes, mut expected: u64) -> bool {
+        while expected != 0 {
+            let mut value = u64::from(first - b'0');
+
+            loop {
+                match value.cmp(&expected) {
+                    Ordering::Less => {
+                        if let Some(next) = iter.next() {
+                            value = value * 10 + u64::from(next - b'0');
+                        } else {
+                            return false;
+                        }
+                    }
+                    Ordering::Equal => {
+                        if let Some(next) = iter.next() {
+                            first = next;
+                            expected -= 1;
+
+                            break;
+                        }
+
+                        return true;
+                    }
+                    Ordering::Greater => return false,
+                }
+            }
+        }
+
+        first == b'0' && iter.all(|c| c == b'0')
+    }
+
+    pub fn split_string(s: String) -> bool {
+        let mut iter = s.bytes();
+
+        let mut value = loop {
+            if let Some(c) = iter.next() {
+                if c != b'0' {
+                    break u64::from(c - b'0');
+                }
+            } else {
+                return false;
+            }
+        };
+
+        while let Some(c) = iter.next() {
+            if Self::check(c, iter.clone(), value - 1) {
+                return true;
+            }
+
+            if let Some(next_value) = value
+                .checked_mul(10)
+                .and_then(|value| value.checked_add(u64::from(c - b'0')))
+            {
+                value = next_value;
+            } else {
+                break;
+            }
+        }
+
+        false
+    }
+}
+
+// ------------------------------------------------------ snip ------------------------------------------------------ //
+
+impl super::Solution for Solution {
+    fn split_string(s: String) -> bool {
+        Self::split_string(s)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn test_solution() {
+        super::super::tests::run::<super::Solution>();
+    }
+}
diff --git a/src/problem_1849_splitting_a_string_into_descending_consecutive_values/mod.rs b/src/problem_1849_splitting_a_string_into_descending_consecutive_values/mod.rs
new file mode 100644
index 00000000..4a8d40db
--- /dev/null
+++ b/src/problem_1849_splitting_a_string_into_descending_consecutive_values/mod.rs
@@ -0,0 +1,26 @@
+pub mod backtracking;
+
+pub trait Solution {
+    fn split_string(s: String) -> bool;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    pub fn run<S: Solution>() {
+        let test_cases = [
+            ("1234", false),
+            ("050043", true),
+            ("9080701", false),
+            ("99999999999999999998", true),
+            ("00000", false),
+            ("64424509442147483647", false),
+            ("10009998", true),
+        ];
+
+        for (s, expected) in test_cases {
+            assert_eq!(S::split_string(s.to_string()), expected);
+        }
+    }
+}