From 482f01ed5ebdcd4e0a9aa764ec4fbf265549f927 Mon Sep 17 00:00:00 2001
From: Janis <janis@nirgendwo.xyz>
Date: Sat, 18 Mar 2023 17:13:18 +0100
Subject: [PATCH] most/least significant element tests/accessors

---
 src/main.zig | 123 ++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 112 insertions(+), 11 deletions(-)

diff --git a/src/main.zig b/src/main.zig
index 93defb2..7916e06 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -237,6 +237,70 @@ const BTree = struct {
             }
         }
 
+        fn find_most_significant_key(self: NodeOrLeaf) Leaf.SearchResult {
+            var node = self;
+            while (true) {
+                switch (node.force()) {
+                    .internal => |internal| {
+                        if (internal.get_edges()[internal.leaf.len]) |child| {
+                            node = child;
+                            continue;
+                        }
+                    },
+                    .leaf => |leaf| {
+                        return .{ .Leaf = .{ .leaf = leaf, .idx = leaf.len - 1 } };
+                    },
+                }
+            }
+        }
+
+        fn find_least_significant_key(self: NodeOrLeaf) Leaf.SearchResult {
+            var node = self;
+            while (true) {
+                switch (node.force()) {
+                    .internal => |internal| {
+                        if (internal.get_edges()[0]) |child| {
+                            node = child;
+                            continue;
+                        }
+                    },
+                    .leaf => |leaf| {
+                        return .{ .Leaf = .{ .leaf = leaf, .idx = 0 } };
+                    },
+                }
+            }
+        }
+
+        fn get_most_significant_value(self: NodeOrLeaf) u32 {
+            switch (self.force()) {
+                .internal => |node| {
+                    if (node.get_edges()[node.leaf.len]) |edge| {
+                        return edge.get_most_significant_value();
+                    } else {
+                        return node.as_leaf().get_values()[node.leaf.len - 1];
+                    }
+                },
+                .leaf => |node| {
+                    return node.get_values()[node.len - 1];
+                },
+            }
+        }
+
+        fn get_least_significant_value(self: NodeOrLeaf) u32 {
+            switch (self.force()) {
+                .internal => |node| {
+                    if (node.get_edges()[0]) |edge| {
+                        return edge.get_least_significant_value();
+                    } else {
+                        return node.as_leaf().get_values()[0];
+                    }
+                },
+                .leaf => |node| {
+                    return node.get_values()[0];
+                },
+            }
+        }
+
         fn dbg(self: NodeOrLeaf) void {
             switch (self) {
                 .internal => |node| {
@@ -343,6 +407,12 @@ const BTree = struct {
             const edges = self.get_edges()[0..values.len];
             std.debug.print("{{ ", .{});
             std.debug.print("[{}] ", .{self.leaf.level});
+
+            // an internal node should have at least B elements
+            if (self.leaf.len < MIN_AFTER_SPLIT) {
+                std.debug.print("[E] ", .{});
+            }
+
             for (values, edges) |v, e| {
                 if (e) |edge| {
                     edge.dbg();
@@ -458,6 +528,11 @@ const BTree = struct {
             Leaf: struct { leaf: *Leaf, idx: u16 },
         };
 
+        fn remove_key(self: *Leaf, key: u32) void {
+            _ = self;
+            _ = key;
+        }
+
         fn find_key(self: *Leaf, key: u32) SearchResult {
             for (self.get_values(), 0..) |v, i| {
                 if (key < v) {
@@ -516,17 +591,6 @@ pub fn main() !void {
     try bw.flush(); // don't forget to flush!
 }
 
-test "btree leaf" {
-    std.testing.refAllDeclsRecursive(BTree);
-    std.testing.refAllDeclsRecursive(BTree.Leaf);
-
-    var leaf = BTree.Leaf{ .ally = std.testing.allocator, .parent = null, .len = 2, .values = [_]u32{ 5, 6, undefined, undefined, undefined } };
-    const values = leaf.get_values();
-
-    std.debug.print("{?}\n", .{leaf});
-    std.debug.print("{any}\n", .{values});
-}
-
 fn printValues(leaf: *BTree.Leaf) void {
     const values = leaf.get_values();
     std.debug.print("{any}\n", .{values});
@@ -608,3 +672,40 @@ test "btree rand insert" {
 
     tree.dbg();
 }
+
+test "btree least most sig value" {
+    std.debug.print("least/most significant values\n", .{});
+
+    var tree = BTree.create(std.testing.allocator);
+    defer tree.destroy();
+
+    for (0..100) |i| {
+        tree.insert(@intCast(u32, i)) catch {
+            std.debug.print("{} already present - ignoring\n", .{i});
+        };
+    }
+    tree.dbg();
+    std.debug.print("\n", .{});
+
+    {
+        const l = tree.root.?.get_least_significant_value();
+        const r = tree.root.?.get_most_significant_value();
+        std.debug.print("{} < {}\n", .{ l, r });
+        std.debug.assert(l == 0);
+        std.debug.assert(r == 99);
+    }
+
+    {
+        const node = tree.root.?;
+        const l = node.find_least_significant_key();
+        const r = node.find_most_significant_key();
+        std.debug.print("{} < {}\n", .{ l, r });
+    }
+
+    {
+        const node = tree.root.?.internal.edges[1].?.force();
+        const l = node.get_least_significant_value();
+        const r = node.get_most_significant_value();
+        std.debug.print("{} < {}\n", .{ l, r });
+    }
+}