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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.
一开始是按照自顶向下的方式来寻找最小值，边界处理有点麻烦，调了几次。
1 public class Solution { 2 public int minimumTotal(List<List<Integer>> triangle) { 3 int len = triangle.size(); 4 int[] dp = new int[len+1]; 5 Arrays.fill(dp,Integer.MAX_VALUE); 6 dp[1] = triangle.get(0).get(0); 7 8 for(int i = 1; i <len; i++){ 9 for(int j = triangle.get(i).size(); j > 0; j--){ 10 dp[j] = triangle.get(i).get(j-1) + Math.min(dp[j],dp[j-1]); 11 } 12 } 13 int min = Integer.MAX_VALUE; 14 for(int i = 1;i <= triangle.size(); i++){ 15 min = Math.min(min,dp[i]); 16 } 17 return min; 18 } 19 }
解法二采用自底向上：
1 public class Solution { 2 public int minimumTotal(List<List<Integer>> triangle) { 3 int len = triangle.size(); 4 int[] dp = new int[len]; 5 for(int i = 0; i< len; i++){ 6 dp[i] = triangle.get(len-1).get(i); 7 } 8 for(int i = len-2; i>=0; i--){ 9 for(int j = 0; j < triangle.get(i).size(); j++){ 10 dp[j] = triangle.get(i).get(j) + Math.min(dp[j],dp[j+1]); 11 } 12 } 13 return dp[0]; 14 } 15 }
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原文地址：http://www.cnblogs.com/guoguolan/p/5638103.html
