Triangle

Change-Id: I048d685c459bb97fe0ccefcd20d0c3788264804f

Triangle.java

@@ -0,0 +1,35 @@
+/*
+ Author:     Andy, [email protected]
+ Date:       May 14, 2013
+ Problem:    Triangle
+ Difficulty: Easy
+ Source:     https://oj.leetcode.com/problems/triangle/
+ Notes:
+ 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.
+
+ Solution: Note that there are n elements in the n-th row (n starts from 1).
+           1. DP. Do not need additional spaces (happen in-place).
+ */
+public class Solution {
+    public int minimumTotal(List<List<Integer>> triangle) {
+        for (int i = triangle.size() - 2; i >= 0; --i) {
+            List<Integer> cur = triangle.get(i);
+            List<Integer> next = triangle.get(i+1);
+            for (int j = 0; j < i + 1; ++j) {
+                cur.set(j, Math.min(next.get(j), next.get(j+1)) + cur.get(j));   
+            }
+        }
+        return triangle == null ? 0 : triangle.get(0).get(0);
+    }
+}