"Added solution for pascal"

Problem1.java

@@ -0,0 +1,27 @@
+Time Complexity: O(n^2)
+Space Complexity: O(n^2)
+solved on leetcode: yes
+any problems faced: no
+// Approach: We can generate the pascal triangle by using the previous row. The first and last element of each row is 1 and the rest of the elements are the sum of the two elements above it in the previous row.
+class Solution {
+    public List<List<Integer>> generate(int numRows) {
+        List<List<Integer>> pascalTriange = new ArrayList<>();
+        List<Integer> previous = new ArrayList<>();
+        previous.add(1);
+        pascalTriange.add(previous);
+        for(int i = 1;i<numRows;i++){
+            List<Integer> temp = new ArrayList<>();
+            for(int j=0;j<=i;j++){
+                if(j==0 || j==i){
+                    temp.add(1);
+                }
+                else{
+                    temp.add(previous.get(j-1) + previous.get(j));
+                }
+            }
+            pascalTriange.add(temp);
+            previous = temp;
+        } 
+        return pascalTriange;
+    }
+}