Leetcode(118) Pascal Triangle

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Description

Given a non-negative integer numRows, generate the first numRows of Pascal’s triangle.

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In Pascal’s triangle, each number is the sum of the two numbers directly above it.

Example:

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Input: 5
Output:
[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

解法

找到计算公式即可：

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if j == 0 or i == j:
	A[i][j] = 1
else:
	A[i][j] = A[i-1][j-1] + A[i-1][j]

具体代码如下：

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