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063.UniquePathsII.cpp
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94 lines (84 loc) · 2.65 KB
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/*Question:
Follow up for "Unique Paths":
Now consider if some obstacles are added to the grids. How many unique paths would there be?
An obstacle and empty space is marked as 1 and 0 respectively in the grid.
For example,
There is one obstacle in the middle of a 3x3 grid as illustrated below.
[
[0,0,0],
[0,1,0],
[0,0,0]
]
The total number of unique paths is 2.
Note: m and n will be at most 100.
Tags: Array, DP
*/
/*思路：
分别处理第一行、第一列以及剩下的元素
*/
//Code:
class Solution {
public:
int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
if (obstacleGrid.empty() || obstacleGrid[0][0]==1)
return 0;
int row = obstacleGrid.size();
int column = obstacleGrid[0].size();
std::vector<int> paths(row*column, 1);
//处理第一行
for (int i = 1; i<column; ++i)
{
if (obstacleGrid[0][i] == 1)
paths[i] = 0;
else
paths[i] = paths[i - 1];
}
//处理第一列
for (int i = 1; i<row; ++i)
{
if (obstacleGrid[i][0] == 1)
paths[i*column] = 0;
else if (i > 0)
paths[i*column] = paths[(i - 1)*column];
}
//处理第一行第一列之外的
for (int i = 1; i<row; ++i)
for (int j = 1; j<column; ++j)
{
if (obstacleGrid[i][j] == 1)
paths[i*column + j] = 0;
else
paths[i*column + j] = paths[(i - 1)*column + j] + paths[i*column + j - 1];
}
return paths[row*column - 1];
}
};
//Code2:
class Solution {
public:
int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
if (obstacleGrid.empty() || obstacleGrid[0].empty())
return 0;
int row = obstacleGrid.size();
int column = obstacleGrid[0].size();
std::vector<int> paths(row*column, 1);
for(int i=0; i < row; ++i)
for(int j=0; j<column; ++j)
{
if(obstacleGrid[i][j] == 1)
paths[i*column+j] = 0;
else
{
if(i>0 && j>0)
paths[i*column + j] = paths[(i - 1)*column + j] + paths[i*column + j - 1];
else if(i==0 && j>0) //第一行
paths[j] = paths[j-1];
else if(j==0 && i>0)
paths[i*column] = paths[(i-1)*column];
else
paths[i*column+j] = 1;
}
}
return paths[row*column - 1];
}
};