feat : unique-paths

Author: ekgns33

unique-paths/ekgns33.java

@@ -0,0 +1,38 @@
+/*
+input : 2D matrix 
+output : the number of possible unique paths
+constraints : 
+1) range of m and n
+[1, 100]
+
+solution 1) dfs?
+move right or move down.
+tc : O(mn)
+sc : O(mn)
+
+solution 2) dp + tabulation
+let dp[i][j] the number of unique paths from starting point.
+    there are only 2 way to get coordinate i, j 
+        1) from i-1, j
+        2) from i, j-1
+dp[i][j] = dp[i-1][j] + dp[i][j-1]
+
+tc : O(mn)
+sc : O(mn)
+ */
+
+class Solution {
+  public int uniquePaths(int m, int n) {
+    int[][] dp = new int[m][n];
+    for(int i = 0; i < m; i++) {
+      for(int j = 0; j < n; j++) {
+        if(i == 0 || j == 0) {
+          dp[i][j] = 1;
+          continue;
+        }
+        dp[i][j] = dp[i][j-1] + dp[i-1][j];
+      }
+    }
+    return dp[m-1][n-1];
+  }
+}