Triangle

fishercoder1534 · fishercoder1534 · commit a2088b569b04 · 2016-12-02T09:26:26.000-08:00
diff --git a/MEDIUM/src/medium/Triangle.java b/MEDIUM/src/medium/Triangle.java
@@ -0,0 +1,28 @@
+package medium;
+import java.util.*;
+public class Triangle {
+
+    public static int minimumTotal(List<List<Integer>> triangle) {
+        /**Looked at this post: https://discuss.leetcode.com/topic/1669/dp-solution-for-triangle, @stellari has a very excellent explanation.
+         * Basically, we use the bottom-up approach, starting from the bottom row of this triangle, and we only need to store the shortest path of each node
+         * from its last row, and keep overwriting it until we reach the top.*/
+        int n = triangle.size();
+        List<Integer> cache = triangle.get(n-1);
+        
+        for (int layer = n-2; layer >= 0; layer--){//for each layer
+            for (int i = 0; i <= layer; i++){//check its very node
+                int value = Math.min(cache.get(i), cache.get(i+1)) + triangle.get(layer).get(i);
+                cache.set(i, value);
+            }
+        }
+        return cache.get(0);
+    }
+    
+    public static void main(String...strings){
+        List<List<Integer>> triangle = new ArrayList();
+        triangle.add(Arrays.asList(1));
+        triangle.add(Arrays.asList(2,3));
+        System.out.println(minimumTotal(triangle));
+    }
+
+}
diff --git a/README.md b/README.md
@@ -99,6 +99,7 @@
 |125|[Valid Palindrome](https://leetcode.com/problems/valid-palindrome/)|[Solution](../../blob/master/EASY/src/easy/ValidPalindrome.java)| O(n)|O(1) | Easy| Two Pointers
 |122|[Best Time to Buy and Sell Stock II](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/)|[Solution](../../blob/master/MEDIUM/src/medium/BestTimeToBuyAndSellStockII.java)| O(n)|O(1) | Medium | Greedy
 |121|[Best Time to Buy and Sell Stock](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)|[Solution](../../blob/master/EASY/src/easy/BestTimeToBuyAndSellStock.java)| O(n)|O(1) | Easy| DP
+|120|[Triangle](https://leetcode.com/problems/triangle/)|[Solution](../../blob/master/MEDIUM/src/medium/Triangle.java)| O(m*n)|O(n) | Medium| DP
 |119|[Pascal's Triangle II](https://leetcode.com/problems/pascals-triangle-ii/)|[Solution](../../blob/master/EASY/src/easy/PascalsTriangleII.java)| O(n^2)|O(1) | Easy| 
 |118|[Pascal's Triangle](https://leetcode.com/problems/pascals-triangle/)|[Solution](../../blob/master/EASY/src/easy/PascalsTriangle.java)| O(n^2)|O(1) | Easy| 
 |117|[Populating Next Right Pointers in Each Node II](https://leetcode.com/problems/populating-next-right-pointers-in-each-node-ii/)|[Solution](../../blob/master/HARD/src/hard/PopulatingNextRightPointersinEachNodeII.java)| O(n)|O(1) | Hard| BFS
