feat: add rust solution to lc problem: No.2251 (#1721)

Author: xzhseh

solution/2200-2299/2251.Number of Flowers in Full Bloom/README.md

@@ -221,6 +221,59 @@ public:
 };
 ```
 
+### **Rust**
+
+```rust
+use std::collections::BTreeMap;
+
+impl Solution {
+    #[allow(dead_code)]
+    pub fn full_bloom_flowers(flowers: Vec<Vec<i32>>, people: Vec<i32>) -> Vec<i32> {
+        let n = people.len();
+
+        // First sort the people vector based on the first item
+        let mut people: Vec<(usize, i32)> = people
+            .into_iter()
+            .enumerate()
+            .map(|x| x)
+            .collect();
+
+        people.sort_by(|lhs, rhs| {
+            lhs.1.cmp(&rhs.1)
+        });
+
+        // Initialize the difference vector
+        let mut diff = BTreeMap::new();
+        let mut ret = vec![0; n];
+
+        for f in flowers {
+            let (left, right) = (f[0], f[1]);
+            diff
+                .entry(left)
+                .and_modify(|x| *x += 1)
+                .or_insert(1);
+
+            diff
+                .entry(right + 1)
+                .and_modify(|x| *x -= 1)
+                .or_insert(-1);
+        }
+
+        let mut sum = 0;
+        let mut i = 0;
+        for (k, v) in diff {
+            while i < n && people[i].1 < k {
+                ret[people[i].0] += sum;
+                i += 1;
+            }
+            sum += v;
+        }
+
+        ret
+    }
+}
+```
+
 ### **Go**
 
 ```go

solution/2200-2299/2251.Number of Flowers in Full Bloom/README_EN.md

@@ -207,6 +207,59 @@ public:
 };
 ```
 
+### **Rust**
+
+```rust
+use std::collections::BTreeMap;
+
+impl Solution {
+    #[allow(dead_code)]
+    pub fn full_bloom_flowers(flowers: Vec<Vec<i32>>, people: Vec<i32>) -> Vec<i32> {
+        let n = people.len();
+
+        // First sort the people vector based on the first item
+        let mut people: Vec<(usize, i32)> = people
+            .into_iter()
+            .enumerate()
+            .map(|x| x)
+            .collect();
+
+        people.sort_by(|lhs, rhs| {
+            lhs.1.cmp(&rhs.1)
+        });
+
+        // Initialize the difference vector
+        let mut diff = BTreeMap::new();
+        let mut ret = vec![0; n];
+
+        for f in flowers {
+            let (left, right) = (f[0], f[1]);
+            diff
+                .entry(left)
+                .and_modify(|x| *x += 1)
+                .or_insert(1);
+
+            diff
+                .entry(right + 1)
+                .and_modify(|x| *x -= 1)
+                .or_insert(-1);
+        }
+
+        let mut sum = 0;
+        let mut i = 0;
+        for (k, v) in diff {
+            while i < n && people[i].1 < k {
+                ret[people[i].0] += sum;
+                i += 1;
+            }
+            sum += v;
+        }
+
+        ret
+    }
+}
+```
+
 ### **Go**
 
 ```go

solution/2200-2299/2251.Number of Flowers in Full Bloom/Solution.rs

@@ -0,0 +1,48 @@
+use std::collections::BTreeMap;
+
+impl Solution {
+    #[allow(dead_code)]
+    pub fn full_bloom_flowers(flowers: Vec<Vec<i32>>, people: Vec<i32>) -> Vec<i32> {
+        let n = people.len();
+
+        // First sort the people vector based on the first item
+        let mut people: Vec<(usize, i32)> = people
+            .into_iter()
+            .enumerate()
+            .map(|x| x)
+            .collect();
+
+        people.sort_by(|lhs, rhs| {
+            lhs.1.cmp(&rhs.1)
+        });
+
+        // Initialize the difference vector
+        let mut diff = BTreeMap::new();
+        let mut ret = vec![0; n];
+
+        for f in flowers {
+            let (left, right) = (f[0], f[1]);
+            diff
+                .entry(left)
+                .and_modify(|x| *x += 1)
+                .or_insert(1);
+
+            diff
+                .entry(right + 1)
+                .and_modify(|x| *x -= 1)
+                .or_insert(-1);
+        }
+
+        let mut sum = 0;
+        let mut i = 0;
+        for (k, v) in diff {
+            while i < n && people[i].1 < k {
+                ret[people[i].0] += sum;
+                i += 1;
+            }
+            sum += v;
+        }
+
+        ret
+    }
+}