Splice ./universe directory into ./

Manually merging:
- README.md: I added the description from universe/README.md into the heading of
  dotfiles/README.md.
- .envrc: dotfiles/.envrc was a superset of universe/.envrc
- .gitignore: Adding some of the ignored patterns from universe/.gitignore to
  dotfiles/.gitignore

Everything else here should be a simple rename.

1 files changed, 87 insertions, 0 deletions

diff --git a/data_structures_and_algorithms/array-traversals.py b/data_structures_and_algorithms/array-traversals.py
new file mode 100644
index 000000000000..35cb4392812e
--- /dev/null
+++ b/data_structures_and_algorithms/array-traversals.py
@@ -0,0 +1,87 @@
+# This is practice for various types of list traversals that turn up.
+
+xs = range(10)
+n = len(xs)
+
+print('---')
+# pythonic left-to-right traversal
+result = ''
+for x in xs:
+    result += str(x)
+print(result)
+
+print('---')
+# left-to-right traversal
+result = ''
+for i in range(n):
+    result += str(xs[i])
+print(result)
+
+print('---')
+# right-to-left traversal
+result = ''
+for i in range(n):
+    result += str(xs[n - 1 - i])
+print(result)
+
+print('---')
+# 2x left-to-right traversal
+result = ''
+for i in range(2 * n):
+    result += str(xs[i % n])
+print(result)
+
+print('---')
+# 2x right-to-left traversal
+result = ''
+for i in range(2 * n):
+    result += str(xs[(n - 1 - i) % n])
+print(result)
+
+################################################################################
+# Table traversals
+################################################################################
+
+table = [[row * 10 + i for i in range(10)] for row in range(3)]
+row_ct = len(table)
+col_ct = len(table[0])
+
+print('---')
+# 3x10 table traversal
+result = ''
+for row in table:
+    r = ''
+    for col in row:
+        r += '{:3d}'.format(col)
+    result += r + '\n'
+print(result[0:-1])
+
+print('---')
+# 3x10 table traversal
+result = ''
+for row in range(row_ct):
+    r = ''
+    for col in range(col_ct):
+        r += '{:3d}'.format(table[row][col])
+    result += r + '\n'
+print(result[0:-1])
+
+print('---')
+# 3x10 table traversal (reverse)
+result = ''
+for row in range(row_ct):
+    r = ''
+    for col in range(col_ct):
+        r += '{:3d}'.format(table[row_ct - 1 - row][col_ct - 1 - col])
+    result += r + '\n'
+print(result)
+
+print('---')
+# 3x10 column-row traversal
+result = ''
+for col in range(col_ct):
+    r = ''
+    for row in range(row_ct):
+        r += '{:3d}'.format(table[row][col])
+    result += r + '\n'
+print(result)