Leetcode-62. Unique Paths and 63. Unique Paths II
Leetcode-62. Unique Paths
题目：
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?
题目太简单，典型的动态规划思想，直接贴代码吧！！！class Solution {
public:
int uniquePaths(int m, int n) {
if (m == 0 || n == 0)return 0;
if (m == 1 || n == 1)return 1;
vectorvec(n,0);
vector>tmp;
for (int i = 0; i < m; i++)tmp.push_back(vec);
for (int i = 0; i < m; i++)tmp[i][0] = 1;
for (int i = 0; i < n; i++)tmp[0][i] = 1;
for (int i = 1; i < m;i++){
for (int j = 1; j < n;j++){
tmp[i][j] = tmp[i - 1][j] + tmp[i][j-1];
}
}
return tmp[m-1][n-1];
}
}; 运行结果：
Submission Result: Accepted More Details
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Leetcode-63. Unique Paths II
题目：
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.
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1.当遇到障碍物时，直接将tmp的值设置为0，并且直接continue跳过去；
2.障碍物时，第一行和第一列不能直接设置成1。因为当障碍物出现在第一行或是第一列时，那么第一行和第一列的后续的格子中的所有值均为0。解答完
毕！！！！
class Solution {
public:
int uniquePathsWithObstacles(vector>& obstacleGrid) {
int row = obstacleGrid.size();
int col = obstacleGrid[0].size();
if (row == 0 || col == 0)return 0;
if (obstacleGrid[0][0] == 1)return 0;//入口被堵死
vectorvec(col, 0);
vector>tmp;
for (int i = 0; i < row; i++)tmp.push_back(vec);
//填表
tmp[0][0] = 1;
for (int i = 0; i < row; i++){
for (int j = 0; j < col; j++){
if (obstacleGrid[i][j] == 1){
tmp[i][j] = 0;
continue;
}
tmp[i][j] = max((i>0 ? tmp[i - 1][j] : 0) + (j>0 ? tmp[i][j - 1] : 0), tmp[i][j]);
}
}
return tmp[row-1][col-1];
}
};