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Cobrust LeetCode Examples

W2 Phase 3 deliverable (ADR-0044). Ten LeetCode-style programs written in Cobrust demonstrating stdin/argv plumbing landed in Phase 2.

Each program reads its input from stdin, computes the result, and writes to stdout — matching the oracle format expected by crates/cobrust-cli/tests/leetcode_corpus_e2e.rs.

Prerequisites

Build the Cobrust compiler:

cargo build -p cobrust-cli

How to run

# Build a .cb file to an executable:
cargo run -p cobrust-cli -- build examples/leetcode/<problem>.cb -o /tmp/<problem>

# Pipe stdin and capture stdout:
printf "<input>\n" | /tmp/<problem>

LC-01 Two Sum

Problem: Given N integers and a target, find two indices i < j such that nums[i] + nums[j] == target.

Input format:

N
nums[0]
nums[1]
...
nums[N-1]
target

Oracle: N=4, [2,7,11,15], target=9 → 0\n1\n

How to run:

cargo run -p cobrust-cli -- build examples/leetcode/two_sum.cb -o /tmp/two_sum
printf "4\n2\n7\n11\n15\n9\n" | /tmp/two_sum
# Output: 0
#         1

LC-02 Reverse String

Problem: Reverse the input string.

Input format: one line with the string.

Oracle: "hello" → "olleh\n"

How to run:

cargo run -p cobrust-cli -- build examples/leetcode/reverse_string.cb -o /tmp/reverse_string
printf "hello\n" | /tmp/reverse_string
# Output: olleh

LC-03 Fibonacci

Problem: Compute F(N) where F(0)=0, F(1)=1, F(N)=F(N-1)+F(N-2).

Input format: one line with integer N.

Oracle: N=10 → "55\n"

How to run:

cargo run -p cobrust-cli -- build examples/leetcode/fibonacci.cb -o /tmp/fibonacci
printf "10\n" | /tmp/fibonacci
# Output: 55

LC-04 Valid Parentheses

Problem: Given a string of ()[]{}, determine if it is balanced.

Input format: one line with the bracket string.

Oracle #1: "()[]{}" → "true\n" Oracle #2: "(]" → "false\n"

How to run:

cargo run -p cobrust-cli -- build examples/leetcode/valid_parentheses.cb -o /tmp/valid_parentheses
printf "()[]{}\n" | /tmp/valid_parentheses   # true
printf "(]\n" | /tmp/valid_parentheses       # false

LC-05 Merge Two Sorted Lists

Problem: Merge two sorted integer lists into one sorted list.

Input format:

N M
list1[0] list1[1] ... list1[N-1]
list2[0] list2[1] ... list2[M-1]

Oracle: N=3 M=3, [1,3,5] [2,4,6] → "1\n2\n3\n4\n5\n6\n"

How to run:

cargo run -p cobrust-cli -- build examples/leetcode/merge_two_sorted_lists.cb -o /tmp/merge_two_sorted_lists
printf "3 3\n1 3 5\n2 4 6\n" | /tmp/merge_two_sorted_lists
# Output: 1 2 3 4 5 6 (one per line)

LC-06 Maximum Subarray (Kadane's Algorithm)

Problem: Find the contiguous subarray with the largest sum.

Input format:

N
nums[0] nums[1] ... nums[N-1]

Oracle: N=9, [-2,1,-3,4,-1,2,1,-5,4] → "6\n"

How to run:

cargo run -p cobrust-cli -- build examples/leetcode/maximum_subarray.cb -o /tmp/maximum_subarray
printf "9\n-2 1 -3 4 -1 2 1 -5 4\n" | /tmp/maximum_subarray
# Output: 6

LC-07 Binary Search

Problem: Search for a target in a sorted array; return its 0-based index or -1 if not found.

Input format:

N
sorted_nums[0] ... sorted_nums[N-1]
target

Oracle: N=6, [-1,0,3,5,9,12], target=9 → "4\n"

How to run:

cargo run -p cobrust-cli -- build examples/leetcode/binary_search.cb -o /tmp/binary_search
printf "6\n-1 0 3 5 9 12\n9\n" | /tmp/binary_search
# Output: 4

LC-08 Climbing Stairs

Problem: Count distinct ways to climb N stairs taking 1 or 2 steps.

Input format: one line with integer N.

Oracle: N=5 → "8\n"

How to run:

cargo run -p cobrust-cli -- build examples/leetcode/climbing_stairs.cb -o /tmp/climbing_stairs
printf "5\n" | /tmp/climbing_stairs
# Output: 8

LC-09 Best Time to Buy and Sell Stock

Problem: Find the maximum profit from one buy-sell transaction.

Input format:

N
prices[0] prices[1] ... prices[N-1]

Oracle: N=6, [7,1,5,3,6,4] → "5\n" (buy at 1, sell at 6)

How to run:

cargo run -p cobrust-cli -- build examples/leetcode/stock_best_time.cb -o /tmp/stock_best_time
printf "6\n7 1 5 3 6 4\n" | /tmp/stock_best_time
# Output: 5

LC-10 Roman to Integer

Problem: Convert a Roman numeral string to its integer value.

Input format: one line with the Roman numeral (e.g. MCMXCIV).

Oracle: "MCMXCIV" → "1994\n"

How to run:

cargo run -p cobrust-cli -- build examples/leetcode/roman_to_integer.cb -o /tmp/roman_to_integer
printf "MCMXCIV\n" | /tmp/roman_to_integer
# Output: 1994

Language features demonstrated

All 10 programs use the ADR-0044 W2 Phase 2/3 source-level surface:

Feature Example
input("") -> str Reading a line from stdin
parse_int(s) -> i64 Parsing integer from string
parse_int_tok(line, i) -> i64 i-th space-separated int
count_toks(line) -> i64 Count of tokens in line
str_len(s) -> i64 Length of string
str_at(s, i) -> str Character at position i
str_ord(c) -> i64 ASCII code of first byte
str_eq_lit(a, "b") -> i64 Compare against literal
print_no_nl(c) Print without trailing newline
list_new(n) -> list[i64] Pre-allocated mutable list
list_set(lst, i, v) Write to list position
list_get(lst, i) -> i64 Read from list position
print_int(n) Print integer + newline
while / if / elif / else Control flow
fn name(args) -> ret: User-defined functions