From b2d2c6d16d4862eb43e86233605d9a63c94c73e6 Mon Sep 17 00:00:00 2001
From: Andrei Navumenka <indy256@gmail.com>
Date: Sun, 7 Jul 2024 14:41:21 -0400
Subject: [PATCH 1/2] Improve java perstistent tree

---
 java/structures/PersistentTree.java | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/java/structures/PersistentTree.java b/java/structures/PersistentTree.java
index b0694f5c..2b9450b5 100644
--- a/java/structures/PersistentTree.java
+++ b/java/structures/PersistentTree.java
@@ -13,10 +13,7 @@ public static class Node {
         Node(Node left, Node right) {
             this.left = left;
             this.right = right;
-            if (left != null)
-                sum += left.sum;
-            if (right != null)
-                sum += right.sum;
+            sum = left.sum + right.sum;
         }
     }
 

From ca773958189d525ab059913227b6461eeeb42696 Mon Sep 17 00:00:00 2001
From: Andrei Navumenka <indy256@gmail.com>
Date: Sun, 7 Jul 2024 15:18:14 -0400
Subject: [PATCH 2/2] Add rust binary search

---
 rust/Cargo.toml            |  4 ++++
 rust/misc/binary_search.rs | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 rust/misc/binary_search.rs

diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 9115b4f4..27937258 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -38,3 +38,7 @@ path = "structures/fenwick_tree.rs"
 [[bin]]
 name = "persistent_tree"
 path = "structures/persistent_tree.rs"
+
+[[bin]]
+name = "binary_search"
+path = "misc/binary_search.rs"
diff --git a/rust/misc/binary_search.rs b/rust/misc/binary_search.rs
new file mode 100644
index 00000000..f72281e1
--- /dev/null
+++ b/rust/misc/binary_search.rs
@@ -0,0 +1,35 @@
+// invariant: f[lo] == false, f[hi] == true
+pub fn binary_search_first_true<F>(f: F, from_inclusive: i32, to_inclusive: i32) -> i32
+where
+    F: Fn(i32) -> bool,
+{
+    let mut lo = from_inclusive - 1;
+    let mut hi = to_inclusive + 1;
+    while hi - lo > 1 {
+        let mid = (lo + hi) / 2;
+        if !f(mid) {
+            lo = mid;
+        } else {
+            hi = mid;
+        }
+    }
+    hi
+}
+
+#[cfg(test)]
+mod tests {
+    use rstest::rstest;
+    use crate::binary_search_first_true;
+
+    #[rstest]
+    #[case(100, 0)]
+    #[case(100, 1)]
+    #[case(100, 50)]
+    #[case(100, 100)]
+    fn basic_test(
+        #[case] n: i32,
+        #[case] pos: i32,
+    ) {
+        assert_eq!(binary_search_first_true(|i| { i >= pos }, 0, n), pos);
+    }
+}