diff --git a/62_unique_paths/problem.md b/62_unique_paths/problem.md
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+## 問題: [62. Unique Paths](https://leetcode.com/problems/unique-paths/description/)
diff --git a/62_unique_paths/step1.md b/62_unique_paths/step1.md
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+# Step 1
+
+- ある地点$grid[i][j]$に辿り着けるルートの数は$grid[i - 1][j]$に辿り着くルートの数と$grid[i][j - 1]$に辿り着くルートの数の和である
+
+```python
+class Solution:
+    def uniquePaths(self, m: int, n: int) -> int:
+        grid = [[1] * n] + [[1] + [0] * (n - 1)] * (m - 1)
+        for i in range(1, m):
+            for j in range(1, n):
+                grid[i][j] = grid[i - 1][j] + grid[i][j - 1]
+        return grid[m - 1][n - 1]
+```
+
+時間計算量: $O(m \times n)$
+
+空間計算量: $O(m \times n)$
diff --git a/62_unique_paths/step2.md b/62_unique_paths/step2.md
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+# Step 2
+
+- 空間計算量を改善する
+
+```python
+class Solution:
+    def uniquePaths(self, m: int, n: int) -> int:
+        row = [1] * n
+        for i in range(1, m):
+            for j in range(1, n):
+                row[j] += row[j - 1]
+        return row[n - 1]
+
+```
+
+時間計算量: $O(m \times n)$
+
+空間計算量: $O(n)$
diff --git a/62_unique_paths/step3.md b/62_unique_paths/step3.md
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+# Step 3
+
+```python
+class Solution:
+    def uniquePaths(self, m: int, n: int) -> int:
+        row = [1] * n
+        for i in range(1, m):
+            for j in range(1, n):
+                row[j] += row[j - 1]
+        return row[n - 1]
+```
+
+1回目: 1分　20秒
+
+2回目: 1分　6秒
+
+3回目: 1分　6秒