public int uniquePaths(int m, int n) {
int [] [] dp = new int[m][n];
//装换公式 dp[m][n] = dp[m-1][n]+dp[m][n-1]
// 初始化
for (int i =0;i<n;i++){
dp[0][i] = 1;
}
for (int j =0;j<m;j++){
dp[j][0] = 1;
}
//
for (int i =1;i<m;i++){
for (int j = 1;j<n;j++){
dp[i][j] = dp[i-1][j] + dp[i][j-1];
}
}
return dp[m-1][n-1];
}