leetcode-118. Pascal's Triangle
2017-01-04 16:55
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leetcode-118. Pascal’s Triangle
题目:Given numRows, generate the first numRows of Pascal’s triangle.
For example, given numRows = 5,
Return
[
[1],
[1,1],
[1,2,1],
[1,3,3,1],
[1,4,6,4,1]
]
解法有很多种。结构都是类似的,每一行两边都是1,所以首尾不需要迭代,只要运算中间的就好,中间的值相当于上一行相邻位置元素之和,不过需要注意范围。
public class Solution { public List<List<Integer>> generate(int numRows) { List<List<Integer>> ret = new ArrayList<List<Integer>>(); if(numRows==0) return ret; List<Integer> list = new ArrayList<Integer>(); list.add(1); ret.add(list); while(--numRows != 0){ List<Integer> replace = new ArrayList<Integer>(); System.out.println(list); replace.add(1); for(int pos = 1; pos < list.size() ; pos++){ replace.add(list.get(pos-1) + (pos < list.size() ? list.get(pos) : 0)); } replace.add(1); ret.add(replace); list = replace; } return ret; } }
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