@@ -210,24 +210,54 @@ public:
210210``` java
211211class Solution {
212212 public int uniquePathsWithObstacles (int [][] obstacleGrid ) {
213- int n = obstacleGrid. length, m = obstacleGrid[0 ]. length;
214- int [][] dp = new int [n][m];
215- 216- for (int i = 0 ; i < m; i++ ) {
217- if (obstacleGrid[0 ][i] == 1 ) break ; // 一旦遇到障碍,后续都到不了
218- dp[0 ][i] = 1 ;
213+ int m = obstacleGrid. length;
214+ int n = obstacleGrid[0 ]. length;
215+ int [][] dp = new int [m][n];
216+ 217+ // 如果在起点或终点出现了障碍,直接返回0
218+ if (obstacleGrid[m - 1 ][n - 1 ] == 1 || obstacleGrid[0 ][0 ] == 1 ) {
219+ return 0 ;
219220 }
220- for ( int i = 0 ; i < n; i ++ ) {
221- if ( obstacleGrid[i][0 ] == 1 ) break ; // //一旦遇到障碍,后续都到不了
222- dp[i][0 ] = 1 ;
221+ 222+ for ( int i = 0 ; i < m && obstacleGrid[i][0 ] == 0 ; i ++ ) {
223+ dp[i][0 ] = 1 ;
223224 }
224- for (int i = 1 ; i < n; i++ ) {
225- for (int j = 1 ; j < m; j++ ) {
226- if (obstacleGrid[i][j] == 1 ) continue ;
227- dp[i][j] = dp[i - 1 ][j] + dp[i][j - 1 ];
225+ for (int j = 0 ; j < n && obstacleGrid[0 ][j] == 0 ; j++ ) {
226+ dp[0 ][j] = 1 ;
227+ }
228+ 229+ for (int i = 1 ; i < m; i++ ) {
230+ for (int j = 1 ; j < n; j++ ) {
231+ dp[i][j] = (obstacleGrid[i][j] == 0 ) ? dp[i - 1 ][j] + dp[i][j - 1 ] : 0 ;
232+ }
233+ }
234+ return dp[m - 1 ][n - 1 ];
235+ }
236+ }
237+ ```
238+ 239+ ``` java
240+ // 空间优化版本
241+ class Solution {
242+ public int uniquePathsWithObstacles (int [][] obstacleGrid ) {
243+ int m = obstacleGrid. length;
244+ int n = obstacleGrid[0 ]. length;
245+ int [] dp = new int [n];
246+ 247+ for (int j = 0 ; j < n && obstacleGrid[0 ][j] == 0 ; j++ ) {
248+ dp[j] = 1 ;
249+ }
250+ 251+ for (int i = 1 ; i < m; i++ ) {
252+ for (int j = 0 ; j < n; j++ ) {
253+ if (obstacleGrid[i][j] == 1 ) {
254+ dp[j] = 0 ;
255+ } else if (j != 0 ) {
256+ dp[j] += dp[j - 1 ];
257+ }
228258 }
229259 }
230- return dp[n - 1 ][m - 1 ] ;
260+ return dp[n - 1 ];
231261 }
232262}
233263```
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