triangle（三角形）——leetcode

题目如下：
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 is11(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.

题解如下：

public static int minimumTotal(ArrayList<ArrayList<Integer>> triangle) {    int []d=new int [1];    d[0]=triangle.get(0).get(0).intValue();    for(int i=1;i<triangle.size();i++) {        d=dp(d,triangle,i);    }    int min=Integer.MAX_VALUE;    for(int i=0;i<d.length;i++) {        if(min>d[i]) {            min=d[i];        }    }    return min;}public static int [] dp(int []d,ArrayList<ArrayList<Integer>> triangle,int now) {    int []p=new int [d.length+1];    p[0]=d[0]+triangle.get(now).get(0).intValue();    p[now]=d[now-1]+triangle.get(now).get(now).intValue();    for(int j=1;j<now;j++) {        int min=d[j-1];        if(d[j]<min) {            min=d[j];        }        p[j]=min+triangle.get(now).get(j).intValue();    }    return p;}