From 84008d9b4eea8a92d57569462ff98fa818ad5a74 Mon Sep 17 00:00:00 2001
From: tiennm99 <tiennm99@outlook.com>
Date: Sun, 7 Dec 2025 23:31:48 +0700
Subject: [PATCH] feat(2025): add day7

---
 2025/day7/day7.go | 88 +++++++++++++++++++++++++++++++++++++++++++++++
 2025/day7/go.mod  |  3 ++
 2 files changed, 91 insertions(+)
 create mode 100644 2025/day7/day7.go
 create mode 100644 2025/day7/go.mod

diff --git a/2025/day7/day7.go b/2025/day7/day7.go
new file mode 100644
index 0000000..6bc25d3
--- /dev/null
+++ b/2025/day7/day7.go
@@ -0,0 +1,88 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strings"
+)
+
+type Pair struct {
+	r, c int
+}
+
+func readInput() []string {
+	data, _ := os.ReadFile("input.txt")
+	content := strings.TrimSpace(string(data))
+	lines := strings.Split(strings.ReplaceAll(string(content), "\r\n", "\n"), "\n")
+
+	return lines
+}
+
+func part1() {
+	lines := readInput()
+	size := len(lines[0])
+	prev := []bool{}
+	for i := range size {
+		prev = append(prev, lines[0][i] == 'S')
+	}
+	result := 0
+	for _, line := range lines[1:] {
+		curr := make([]bool, size)
+		count := 0
+		for i := range size {
+			if prev[i] {
+				if line[i] == '^' {
+					if i-1 >= 0 {
+						curr[i-1] = true
+					}
+					if i+1 < size {
+						curr[i+1] = true
+					}
+					count++
+				} else {
+					curr[i] = true
+				}
+			}
+		}
+		// fmt.Println(count)
+		result += count
+		prev = curr
+	}
+
+	fmt.Printf("%d\n", result)
+}
+
+func part2() {
+	lines := readInput()
+	w, h := len(lines[0]), len(lines)
+	cache := make(map[Pair]int)
+	var count func(r, c int) int
+	count = func(r, c int) int {
+		if c < 0 || c >= w {
+			return 0
+		}
+		if r == h {
+			return 1
+		}
+		if _, ok := cache[Pair{r, c}]; ok {
+			return cache[Pair{r, c}]
+		}
+		if lines[r][c] == '^' {
+			result := count(r+1, c-1) + count(r+1, c+1)
+			cache[Pair{r, c}] = result
+			return result
+		}
+		result := count(r+1, c)
+		cache[Pair{r, c}] = result
+		return result
+	}
+	r0, c0 := 0, strings.IndexByte(lines[0], 'S')
+	result := count(r0, c0)
+
+	fmt.Printf("%d\n", result)
+}
+
+func main() {
+	part1()
+	part2()
+}
diff --git a/2025/day7/go.mod b/2025/day7/go.mod
new file mode 100644
index 0000000..cff27b2
--- /dev/null
+++ b/2025/day7/go.mod
@@ -0,0 +1,3 @@
+module day7
+
+go 1.23.4