118 Pascal_Triangle

Easy/Pascal_Triangle.java

@@ -0,0 +1,57 @@
+/**
+ * Pascal's Triangle
+ * Given numRows, generate the first numRows of Pascal's triangle.
+   For example, given numRows = 5,
+   Return
+
+	    [
+		     [1],
+		    [1,1],
+		   [1,2,1],
+		  [1,3,3,1],
+		 [1,4,6,4,1]
+		]
+
+	Analysis :
+	 using dp
+ */
+
+import java.util.*;
+
+public class Pascal_Triangle {
+    public static List<List<Integer>> generate(int numRows) {
+
+        List<List<Integer>> res = new ArrayList<List<Integer>>();
+        ArrayList<Integer> member = new ArrayList<Integer>();
+        if(numRows <= 0){
+            return res;
+        }
+        member.add(1);
+        res.add( member);
+        return generateArray(res, numRows-1);
+    }
+
+	public static List<List<Integer>> generateArray(List<List<Integer>> res, int n){
+        if(n == 0){
+            return res;
+        }
+        else{
+           List<Integer> resLast= new ArrayList<Integer>(); 
+           ArrayList<Integer> newMember = new ArrayList<Integer>(); 
+           resLast = res.get(res.size()-1);
+           newMember.add(1);
+           for(int i = 0; i < resLast.size()-1; i++){
+               int temp = resLast.get(i) + resLast.get(i+1);
+               newMember.add(temp);
+           }
+           newMember.add(1);
+           res.add(newMember);
+           return generateArray(res, n-1);
+        }
+    }
+	public static void main(String[] args) {
+		// TODO Auto-generated method stub
+		System.out.print(generate(5));
+	}
+
+}