diff --git a/Cargo.lock b/Cargo.lock
index 1400ea9..9395000 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4,6 +4,10 @@
 name = "binary_tree_postorder_traversal"
 version = "0.1.0"
 
+[[package]]
+name = "course_schedule_iii"
+version = "0.1.0"
+
 [[package]]
 name = "edit_distance"
 version = "0.1.0"
@@ -28,6 +32,14 @@ version = "0.1.0"
 name = "merge_sorted_array"
 version = "0.1.0"
 
+[[package]]
+name = "non_decreasing_array"
+version = "0.1.0"
+
+[[package]]
+name = "prefix_and_suffix_search"
+version = "0.1.0"
+
 [[package]]
 name = "reverse_integer"
 version = "0.1.0"
diff --git a/Cargo.toml b/Cargo.toml
index 6187d46..24e2beb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,4 +13,7 @@ members = [
     "reverse_words_in_a_string_iii",
     "edit_distance",
     "running_sum_of_1d_array",
+    "course_schedule_iii",
+    "prefix_and_suffix_search",
+    "non_decreasing_array",
 ]
diff --git a/course_schedule_iii/Cargo.toml b/course_schedule_iii/Cargo.toml
new file mode 100644
index 0000000..629cb7d
--- /dev/null
+++ b/course_schedule_iii/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "course_schedule_iii"
+version = "0.1.0"
+authors = ["Ryan Li <conbas2019@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/course_schedule_iii/src/lib.rs b/course_schedule_iii/src/lib.rs
new file mode 100644
index 0000000..60e8c64
--- /dev/null
+++ b/course_schedule_iii/src/lib.rs
@@ -0,0 +1,81 @@
+/*
+ * [Explore - LeetCode](https://leetcode.com/explore/featured/card/may-leetcoding-challenge-2021/598/week-1-may-1st-may-7th/3729/)
+ */
+
+use std::collections::BinaryHeap;
+
+pub struct Solution {}
+
+impl Solution {
+    pub fn schedule_course(courses: Vec<Vec<i32>>) -> i32 {
+        // order by deadline
+        let mut courses = courses;
+        courses.sort_by(|x, y| x[1].cmp(&y[1]));
+        let mut deadline = 0;
+        let mut selected = BinaryHeap::new();
+        for c in courses.iter() {
+            let duration = c[0];
+            let last_day = c[1];
+            if deadline + duration <= last_day {
+                selected.push(c);
+                deadline += duration;
+                continue;
+            }
+            if selected.len() > 0
+                && selected.peek().unwrap()[0] > duration
+                && deadline - selected.peek().unwrap()[0] + duration <= last_day
+            {
+                let max = selected.pop().unwrap();
+                selected.push(c);
+                deadline = deadline - max[0] + duration;
+                continue;
+            }
+        }
+        selected.len() as i32
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_example_1() {
+        let courses = vec![
+            vec![100, 200],
+            vec![200, 1300],
+            vec![1000, 1250],
+            vec![2000, 3200],
+        ];
+        assert_eq!(Solution::schedule_course(courses), 3);
+    }
+
+    #[test]
+    fn test_example_2() {
+        let courses = vec![vec![1, 2]];
+        assert_eq!(Solution::schedule_course(courses), 1);
+    }
+
+    #[test]
+    fn test_example_3() {
+        let courses = vec![vec![3, 2], vec![4, 3]];
+        assert_eq!(Solution::schedule_course(courses), 0);
+    }
+
+    #[test]
+    fn test_submission_1() {
+        let courses = vec![
+            vec![7, 16],
+            vec![2, 3],
+            vec![3, 12],
+            vec![3, 14],
+            vec![10, 19],
+            vec![10, 16],
+            vec![6, 8],
+            vec![6, 11],
+            vec![3, 13],
+            vec![6, 16],
+        ];
+        assert_eq!(Solution::schedule_course(courses), 4);
+    }
+}
diff --git a/non_decreasing_array/Cargo.toml b/non_decreasing_array/Cargo.toml
new file mode 100644
index 0000000..f4cf175
--- /dev/null
+++ b/non_decreasing_array/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "non_decreasing_array"
+version = "0.1.0"
+authors = ["Ryan Li <conbas2019@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/non_decreasing_array/src/lib.rs b/non_decreasing_array/src/lib.rs
new file mode 100644
index 0000000..70f1839
--- /dev/null
+++ b/non_decreasing_array/src/lib.rs
@@ -0,0 +1,70 @@
+/*
+ * https://leetcode.com/explore/challenge/card/may-leetcoding-challenge-2021/598/week-1-may-1st-may-7th/3731/
+ */
+
+pub struct Solution {}
+
+impl Solution {
+    pub fn check_possibility(nums: Vec<i32>) -> bool {
+        Self::check_in_sort(nums.clone()) || Self::check_reversed(nums.clone())
+    }
+
+    fn check_in_sort(mut nums: Vec<i32>) -> bool {
+        let mut increase_exists = false;
+        for i in 0..nums.len() - 1 {
+            if nums[i] <= nums[i + 1] {
+                continue;
+            }
+            if increase_exists {
+                return false;
+            }
+            nums[i + 1] = nums[i];
+            increase_exists = true;
+        }
+        true
+    }
+
+    fn check_reversed(mut nums: Vec<i32>) -> bool {
+        let mut increase_exists = false;
+        for i in (0..nums.len() - 1).rev() {
+            if nums[i] <= nums[i + 1] {
+                continue;
+            }
+            if increase_exists {
+                return false;
+            }
+            nums[i] = nums[i + 1];
+            increase_exists = true;
+        }
+        true
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn example_1() {
+        let nums = vec![4, 2, 3];
+        assert!(Solution::check_possibility(nums));
+    }
+
+    #[test]
+    fn example_2() {
+        let nums = vec![4, 2, 1];
+        assert!(!Solution::check_possibility(nums));
+    }
+
+    #[test]
+    fn submission_1() {
+        let nums = vec![3, 4, 2, 3];
+        assert!(!Solution::check_possibility(nums));
+    }
+
+    #[test]
+    fn submission_2() {
+        let nums = vec![5, 7, 1, 8];
+        assert!(Solution::check_possibility(nums));
+    }
+}
diff --git a/prefix_and_suffix_search/Cargo.toml b/prefix_and_suffix_search/Cargo.toml
new file mode 100644
index 0000000..fbbe109
--- /dev/null
+++ b/prefix_and_suffix_search/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "prefix_and_suffix_search"
+version = "0.1.0"
+authors = ["Ryan Li <conbas2019@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/prefix_and_suffix_search/src/lib.rs b/prefix_and_suffix_search/src/lib.rs
new file mode 100644
index 0000000..781de2e
--- /dev/null
+++ b/prefix_and_suffix_search/src/lib.rs
@@ -0,0 +1,150 @@
+/*
+ * [Explore - LeetCode](https://leetcode.com/explore/challenge/card/may-leetcoding-challenge-2021/598/week-1-may-1st-may-7th/3728/)
+ *
+ * Your WordFilter object will be instantiated and called as such:
+ * let obj = WordFilter::new(words);
+ * let ret_1: i32 = obj.f(prefix, suffix);
+ */
+
+#[derive(Clone)]
+struct Trie {
+    children: Vec<Option<Box<Trie>>>,
+    index: i32,
+}
+
+impl Trie {
+    fn get_char_index(c: char) -> usize {
+        if c as usize >= 'a' as usize && c as usize <= 'z' as usize {
+            c as usize - 'a' as usize
+        } else {
+            26
+        }
+    }
+
+    fn new() -> Self {
+        Self {
+            children: vec![None; 27],
+            index: -1,
+        }
+    }
+
+    fn add(&mut self, index: usize, chars: &str) {
+        match chars.chars().nth(0) {
+            None => (),
+            Some(c) => {
+                let c_index = Self::get_char_index(c);
+                let child = self.children[c_index].get_or_insert(Box::new(Self::new()));
+                child.add(index, &chars[1..]);
+            }
+        }
+        self.index = index as i32; // mark index on the whole branch
+    }
+
+    fn search(&self, chars: &str) -> i32 {
+        match chars.chars().nth(0) {
+            None => self.index,
+            Some(c) => {
+                let c_index = Self::get_char_index(c);
+                match &self.children[c_index] {
+                    None => -1,
+                    Some(child) => child.search(&chars[1..]),
+                }
+            }
+        }
+    }
+}
+
+pub struct WordFilter {
+    trie: Trie,
+}
+
+impl WordFilter {
+    pub fn new(words: Vec<String>) -> Self {
+        let mut trie = Trie::new();
+        for (index, word) in words.iter().enumerate() {
+            for pattern in Self::all_patterns(word).iter() {
+                trie.add(index, pattern);
+            }
+        }
+        WordFilter { trie }
+    }
+
+    fn all_patterns(word: &str) -> Vec<String> {
+        let mut res = vec![];
+        for i in 0..word.len() {
+            res.push(String::new() + &word[i..word.len()] + "#" + &word);
+        }
+        res
+    }
+
+    pub fn f(&self, prefix: String, suffix: String) -> i32 {
+        self.trie.search(&(String::new() + &suffix + "#" + &prefix))
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_trie() {
+        let mut root = Trie::new();
+        root.add(0, "foo");
+        root.add(1, "bar");
+        root.add(3, "biz");
+        assert_eq!(root.search("foo"), 0);
+        assert_eq!(root.search("bar"), 1);
+        assert_eq!(root.search("biz"), 3);
+        assert_eq!(root.search("buz"), -1);
+        assert_eq!(root.search("fo"), 0);
+        assert_eq!(root.search("b"), 3);
+    }
+
+    #[test]
+    fn example_1() {
+        let words = vec!["apple"].iter().map(|s| s.to_string()).collect();
+        let prefix = "a".to_string();
+        let suffix = "e".to_string();
+        let expected = 0;
+        assert_eq!(WordFilter::new(words).f(prefix, suffix), expected);
+    }
+
+    #[test]
+    fn submission_1() {
+        let words = vec![
+            "cabaabaaaa",
+            "ccbcababac",
+            "bacaabccba",
+            "bcbbcbacaa",
+            "abcaccbcaa",
+            "accabaccaa",
+            "cabcbbbcca",
+            "ababccabcb",
+            "caccbbcbab",
+            "bccbacbcba",
+        ]
+        .iter()
+        .map(|w| w.to_string())
+        .collect::<Vec<String>>();
+        let patterns = vec![
+            vec!["bccbacbcba", "a"],
+            vec!["ab", "abcaccbcaa"],
+            vec!["a", "aa"],
+            vec!["cabaaba", "abaaaa"],
+            vec!["cacc", "accbbcbab"],
+            vec!["ccbcab", "bac"],
+            vec!["bac", "cba"],
+            vec!["ac", "accabaccaa"],
+            vec!["bcbb", "aa"],
+            vec!["ccbca", "cbcababac"],
+        ]
+        .iter()
+        .map(|p| vec![p[0].to_string(), p[1].to_string()])
+        .collect::<Vec<Vec<String>>>();
+        let result = patterns
+            .iter()
+            .map(|p| WordFilter::new(words.clone()).f(p[0].clone(), p[1].clone()))
+            .collect::<Vec<i32>>();
+        assert_eq!(result, vec![9, 4, 5, 0, 8, 1, 2, 5, 3, 1])
+    }
+}