20240723 Finished

src/problem/mod.rs

@@ -182,3 +182,4 @@ mod p153_find_minimum_in_rotated_sorted_array;
 mod p215_kth_largest_element_in_an_array;
 mod p502_ipo;
 mod p373_find_k_pairs_with_smallest_sums;
+mod p295_find_median_from_data_stream;

src/problem/p295_find_median_from_data_stream.rs

@@ -0,0 +1,100 @@
+/**
+ * [295] Find Median from Data Stream
+ */
+pub struct Solution {}
+
+// submission codes start here
+use std::{cmp::Reverse, collections::BinaryHeap};
+
+#[derive(Debug)]
+struct MedianFinder {
+    left: BinaryHeap<i32>,
+    right: BinaryHeap<Reverse<i32>>
+}
+
+
+/**
+ * `&self` means the method takes an immutable reference.
+ * If you need a mutable reference, change it to `&mut self` instead.
+ */
+impl MedianFinder {
+
+    fn new() -> Self {
+        Self {
+            left: BinaryHeap::new(),
+            right: BinaryHeap::new()
+        }
+    }
+    
+    fn add_num(&mut self, num: i32) {
+        // 保证如下的状态
+        // left.len = right.len + 1
+        // left.len = right.len
+        
+        if self.left.len() > self.right.len() {
+            // 此时左边必然有数
+            let left_peek = *self.left.peek().unwrap();
+            
+            if num >= left_peek {
+                self.right.push(Reverse(num))
+            } else { 
+                self.right.push(Reverse(left_peek));
+                self.left.pop();
+                self.left.push(num);
+            }
+        } else {
+            // 判空
+            if self.left.is_empty() {
+                self.left.push(num);
+            } else { 
+                // 此时必然两端都有数
+                let right_peek = self.right.peek().unwrap().0;
+                
+                if num <= right_peek {
+                    self.left.push(num);
+                } else { 
+                    self.left.push(right_peek);
+                    self.right.pop();
+                    self.right.push(Reverse(num));
+                }
+            }
+        }
+    }
+    
+    fn find_median(&self) -> f64 {
+        return if self.left.len() == self.right.len() {
+            (*self.left.peek().unwrap() as f64 + self.right.peek().unwrap().0 as f64) / 2f64
+        } else { 
+            *self.left.peek().unwrap() as f64
+        }
+    }
+}
+
+/**
+ * Your MedianFinder object will be instantiated and called as such:
+ * let obj = MedianFinder::new();
+ * obj.add_num(num);
+ * let ret_2: f64 = obj.find_median();
+ */
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_295() {
+        let mut finder = MedianFinder::new();
+        
+        finder.add_num(1);
+        finder.add_num(2);
+        
+        assert_eq!(1.5, finder.find_median());
+        
+        finder.add_num(3);
+        finder = dbg!(finder);
+        
+        assert_eq!(2f64, finder.find_median());
+    }
+}