Pascal's Triangle II
2015-01-26 21:18
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Given an index k, return the kth row of the Pascal's triangle.
For example, given k = 3,
Return
完成Pascal's Triangle问题,这个就不难了吧~
For example, given k = 3,
Return
[1,3,3,1].
完成Pascal's Triangle问题,这个就不难了吧~
public class Solution { public List<Integer> getRow(int rowIndex) { int numRows = rowIndex+1; List<List<Integer>>triangle_list = new ArrayList<List<Integer>>(); //初始化第一和第二行 List<Integer>list1 = new ArrayList<Integer>(); List<Integer>list2 = new ArrayList<Integer>(); list1.add(1); list2.add(1); list2.add(1); //分情况讨论 if(numRows==1){ triangle_list.add(list1); } if(numRows==2){ triangle_list.add(list1); triangle_list.add(list2); } if(numRows>2){ triangle_list.add(list1); triangle_list.add(list2); for(int i=2;i<numRows;i++){//i是行标对应外层list下标 List<Integer>list3 = triangle_list.get(i-1); List<Integer>list4 = new ArrayList<Integer>(); list4.add(1); for(int j=1;j<=i-1;j++){//根据杨辉三角用上一行list3来计算当前行list4 list4.add(list3.get(j-1)+list3.get(j)); } list4.add(1); triangle_list.add(list4); } } return triangle_list.get(rowIndex); } }
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