LeetCode--No.118--Pascal's Triangle

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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]]

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思路上没什么需要说的。需要注意的是ArrayList的使用。

public class Solution {    public List<List<Integer>> generate(int numRows) {        List<List<Integer>> res = new ArrayList<List<Integer>>();        List<Integer> pre = new ArrayList<Integer>();        if (numRows <= 0)            return res;        else{            pre.add(1);            res.add(pre);        }        for(int i = 1; i < numRows; i++){            List<Integer> curr = new ArrayList<Integer>();            curr.add(1);            for(int j = 0; j < pre.size()-1; j++){                curr.add(pre.get(j) + pre.get(j+1));            }            curr.add(1);            res.add(curr);            pre = curr;        }        return res;    }}

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