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LeetCode Unique Paths

A robot is located at the top-left corner of a m x n grid (marked ‘Start‘ in the diagram below).

The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked ‘Finish‘ in the diagram below).

How many possible unique paths are there?

Above is a 3 x 7 grid. How many possible unique paths are there?

Note: m and n will be at most 100.

 

分两种情况讨论,每次只有往下走或者往右走,那么f(m,n)=f(m-1.n)+f(m,n-1).一开始直接使用递归,超时了。 应该存在数组里。

 1 public class Solution { 2     public int uniquePaths(int m, int n) { 3             int[][] f = new int[m][n]; 4             for (int i = 0; i < n; i++) { 5                 f[0][i]=1; 6             } 7              8             for (int i = 0; i < m; i++) { 9                 f[i][0]=1;10             }11             12             for (int i = 1; i < m; i++) {13                 for (int j = 1; j < n; j++) {14                     f[i][j]=f[i-1][j]+f[i][j-1];15                 }16             }17     return f[m-1][n-1];18     }19 }

 

LeetCode Unique Paths