120 triangle

Author: Lei Cao

README.md

@@ -116,7 +116,7 @@ LeetCode
 |123|[Best Time to Buy and Sell Stock III](https://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/)| [C++](./algorithms/bestTimeToBuyAndSellStock/bestTimeToBuyAndSellStock.III.cpp)|Hard|
 |122|[Best Time to Buy and Sell Stock II](https://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/)| [C++](./algorithms/bestTimeToBuyAndSellStock/bestTimeToBuyAndSellStock.II.cpp)|Medium|
 |121|[Best Time to Buy and Sell Stock](https://oj.leetcode.com/problems/best-time-to-buy-and-sell-stock/)| [C++](./algorithms/bestTimeToBuyAndSellStock/bestTimeToBuyAndSellStock.cpp)|Medium|
-|120|[Triangle](https://oj.leetcode.com/problems/triangle/)| [C++](./algorithms/triangle/triangle.cpp)|Medium|
+|120|[Triangle](https://oj.leetcode.com/problems/triangle/)| [C++](./algorithms/triangle/triangle.cpp), [C++](./algorithms-java/src/dynamicProgramming/triangle/triangle.java)|Medium|
 |119|[Pascal's Triangle II](https://oj.leetcode.com/problems/pascals-triangle-ii/)| [C++](./algorithms/pascalTriangle/pascalTriangle.II.cpp)|Easy|
 |118|[Pascal's Triangle](https://oj.leetcode.com/problems/pascals-triangle/)| [C++](./algorithms/pascalTriangle/pascalTriangle.cpp)|Easy|
 |117|[Populating Next Right Pointers in Each Node II](https://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/)| [C++](./algorithms/populatingNextRightPointersInEachNode/populatingNextRightPointersInEachNode.II.cpp)|Hard|

algorithms-java/src/dynamicProgramming/triangle/triangle.java

@@ -0,0 +1,97 @@
+// Source : https://oj.leetcode.com/problems/triangle/
+// Inspired by : http://www.jiuzhang.com/solutions/triangle/
+// Author : Lei Cao
+// Date   : 2015-10-12
+
+/**********************************************************************************
+ *
+ * Given a triangle, find the minimum path sum from top to bottom.
+ * Each step you may move to adjacent numbers on the row below.
+ *
+ * For example, given the following triangle
+ *
+ * [
+ *      [2],
+ *     [3,4],
+ *    [6,5,7],
+ *   [4,1,8,3]
+ * ]
+ *
+ * The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11).
+ *
+ * Note:
+ * Bonus point if you are able to do this using only O(n) extra space, where n is the total number of rows in the triangle.
+ *
+ *
+ **********************************************************************************/
+
+package dynamicProgramming.triangle;
+
+import java.util.List;
+
+/**
+ * Created by leicao on 12/10/15.
+ */
+public class triangle {
+    /**
+     * @param triangle: a list of lists of integers.
+     * @return: An integer, minimum path sum.
+     */
+    public int minimumTotal1(List<List<Integer>> triangle) {
+        if (triangle == null) {
+            return 0;
+        }
+        int rows = triangle.size();
+        int[][] matrix = new int[rows][rows];
+        matrix[0][0] = triangle.get(0).get(0);
+        for (int i = 1; i < rows; i++) {
+            matrix[i][0] = triangle.get(i).get(0) + matrix[i-1][0];
+        }
+
+        for (int i = 1; i < rows; i++) {
+            matrix[i][i] = triangle.get(i).get(i) + matrix[i - 1][i - 1];
+        }
+
+        for (int i = 1; i < rows; i++) {
+            for (int j = 1; j < i; j++) {
+                matrix[i][j] = Math.min(matrix[i-1][j-1], matrix[i-1][j]) + triangle.get(i).get(j);
+            }
+        }
+        int minimum = matrix[rows - 1][0];
+        for (int i = 1; i < rows; i++) {
+            if (matrix[rows - 1][i] < minimum) {
+                minimum = matrix[rows - 1][i];
+            }
+        }
+        return minimum;
+    }
+
+    public int minimumTotal2(int[][] triangle) {
+        if (triangle == null) {
+            return 0;
+        }
+        int rows = triangle.length;
+        int[][] matrix = new int[rows][rows];
+        matrix[0][0] = triangle[0][0];
+        for (int i = 1; i < rows; i++) {
+            matrix[i][0] = triangle[i][0] + matrix[i-1][0];
+        }
+
+        for (int i = 1; i < rows; i++) {
+            matrix[i][i] = triangle[i][i] + matrix[i - 1][i - 1];
+        }
+
+        for (int i = 1; i < rows; i++) {
+            for (int j = 1; j < i; j++) {
+                matrix[i][j] = Math.min(matrix[i-1][j-1], matrix[i-1][j]) + triangle[i][j];
+            }
+        }
+        int minimum = matrix[rows - 1][0];
+        for (int i = 1; i < rows; i++) {
+            if (matrix[rows - 1][i] < minimum) {
+                minimum = matrix[rows - 1][i];
+            }
+        }
+        return minimum;
+    }
+}

algorithms-java/src/dynamicProgramming/triangle/triangleTest.java

@@ -0,0 +1,32 @@
+package dynamicProgramming.triangle;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+/**
+ * Created by leicao on 15/10/15.
+ */
+public class triangleTest {
+
+    @Test
+    public void testMinimumTotal() throws Exception {
+        int[][][] inputes = {
+            {
+                {2},
+                {3,4},
+                {6,5,7},
+                {4,1,8,3},
+            }
+        };
+
+        int[] results = {11};
+
+        for (int i = 0; i < results.length; i++) {
+            triangle t = new triangle();
+            int r = t.minimumTotal2(inputes[i]);
+            assertEquals(results[i], r);
+        }
+
+    }
+}