62. Unique Paths

Edited by Charles

Medium · Python · Dynamic Programming

Problem

Read the original problem on LeetCode.

The official page contains the problem statement, examples, and constraints.

Explanation, examples & other approaches

Core idea

Recall 70. Climbing Stairs for the core idea. Emphasis: the initialization. Consider the boundaries, say grid[0][j] and grid[i][0], there is only one way to reach the places along these boundaries.

Original study notes follow, including intermediate snippets and earlier attempts.

Note:

1. Recall 70. Climbing Stairs for the core idea.
2. Emphasis: the initialization. Consider the boundaries, say grid[0][j] and grid[i][0], there is only one way to reach the places along these boundaries.

Study record

Field	Value
Attempts	1
Mastery	❚
The Latest Attempt	February 2, 2026

Python solution

class Solution:
    def uniquePaths(self, m: int, n: int) -> int:
        grid = [[1] * n for _ in range(m)]

        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[-1][-1]

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