27
07/2015
[LeetCode] Unique Paths
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.
解题思路：
数学题。共有路径数C(m-1 + n - 1, n-1)。计算的时候会用到阶层运算，因此要用longlong类型防止溢出，而且需要尽量先做除法运算。
class Solution {
public:
int uniquePaths(int m, int n) {
long long result = 1;
if(m<=1 || n<=1){
return result;
}
int j=n-1;
for(int i=m+n-2; i>=m; i--){
while(j>1 && result%j==0){
result = result/j;
j--;
}
result = result * i;
}
while(j>1 && result%j==0){
result = result/j;
j--;
}
return (int)result;
}
};转载请注明：康瑞部落 » [LeetCode] Unique Paths
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