add zig codes for Section 'Space Complexity' and 'Space Time Tradeoff'

codes/zig/include/ListNode.zig

@@ -0,0 +1,20 @@
+// File: ListNode.zig
+// Created Time: 2023-01-07
+// Author: sjinzh (sjinzh@gmail.com)
+
+const std = @import("std");
+
+// Definition for a singly-linked list node
+pub fn ListNode(comptime T: type) type {
+    return struct {
+        const Self = @This();
+        
+        val: T = 0,
+        next: ?*Self = null,
+
+        // Initialize a list node with specific value
+        pub fn init(self: *Self, x: i32) void {
+            self.val = x;
+        }
+    };
+}

codes/zig/include/PrintUtil.zig

@@ -1,13 +1,72 @@
-// File: TreeNode.zig
+// File: PrintUtil.zig
 // Created Time: 2023-01-07
 // Author: sjinzh (sjinzh@gmail.com)
 
 const std = @import("std");
+const ListNode = @import("ListNode.zig").ListNode;
+const TreeNode = @import("TreeNode.zig").TreeNode;
 
-// Print an Array
+// Print an array
 pub fn printArray(comptime T: type, nums: []T) void {
     std.debug.print("[", .{});
-    for (nums) |num, j| {
-        std.debug.print("{}{s}", .{num, if (j == nums.len-1) "]\n" else ", " });
-     }
+    if (nums.len > 0) {
+        for (nums) |num, j| {
+            std.debug.print("{}{s}", .{num, if (j == nums.len-1) "]\n" else ", " });
+        }
+    } else {
+        std.debug.print("]", .{});
+        std.debug.print("\n", .{});
+    }
 }
+
+// This tree printer is borrowed from TECHIE DELIGHT
+// https://www.techiedelight.com/c-program-print-binary-tree/
+const Trunk = struct {
+    prev: ?*Trunk = null,
+    str: []const u8 = undefined,
+    
+    pub fn init(self: *Trunk, prev: ?*Trunk, str: []const u8) void {
+        self.prev = prev;
+        self.str = str;
+    }
+};
+
+// Helper function to print branches of the binary tree
+pub fn showTrunks(p: ?*Trunk) void {
+    if (p == null) return;
+    showTrunks(p.?.prev);
+    std.debug.print("{s}", .{p.?.str});
+}
+
+// The interface of the tree printer
+// Print a binary tree
+pub fn printTree(root: ?*TreeNode(i32), prev: ?*Trunk, isLeft: bool) !void {
+    if (root == null) {
+        return;
+    }
+
+    var prev_str = "    ";
+    var trunk = Trunk{.prev = prev, .str = prev_str};
+
+    try printTree(root.?.right, &trunk, true);
+   
+    if (prev == null) {
+        trunk.str = "———";
+    } else if (isLeft) {
+        trunk.str = "/———";
+        prev_str = "   |";
+    } else {
+        trunk.str = "\\———";
+        prev.?.str = prev_str;
+    }
+
+    showTrunks(&trunk);
+    std.debug.print(" {}\n", .{root.?.val});
+
+    if (prev) |_| {
+        prev.?.str = prev_str;
+    }
+    trunk.str = "   |";
+
+    try printTree(root.?.left, &trunk, false);
+}

codes/zig/include/TreeNode.zig

@@ -0,0 +1,21 @@
+// File: TreeNode.zig
+// Created Time: 2023-01-07
+// Author: sjinzh (sjinzh@gmail.com)
+
+const std = @import("std");
+
+// Definition for a binary tree node
+pub fn TreeNode(comptime T: type) type {
+    return struct {
+        const Self = @This();
+
+        val: T = undefined,
+        left: ?*Self = null,
+        right: ?*Self = null,
+
+        // Initialize a tree node with specific value
+        pub fn init(self: *Self, x: i32) void {
+            self.val = x;
+        }
+    };   
+}

codes/zig/include/include.zig

@@ -1,5 +1,7 @@
 // File: include.zig
-// Created Time: 2023-01-04
+// Created Time: 2023-01-07
 // Author: sjinzh (sjinzh@gmail.com)
 
-pub const PrintUtil = @import("PrintUtil.zig");
+pub const PrintUtil = @import("PrintUtil.zig");
+pub const ListNode = @import("ListNode.zig").ListNode;
+pub const TreeNode = @import("TreeNode.zig").TreeNode;