Description
Given a non-negative integer numRows, generate the first numRows of Pascal’s triangle.
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]
]
|
Solution
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| class Solution {
public List<List<Integer>> generate(int numRows) {
List<List<Integer>> res = new ArrayList<>();
if (numRows == 0) return res;
res.add(new ArrayList<Integer>());
res.get(0).add(1);
if (numRows == 1) return res;
res.add(new ArrayList<Integer>());
res.get(1).add(1);
res.get(1).add(1);
if (numRows == 2) return res;
for (int i = 3; i <= numRows; i++){
List<Integer> preLine= res.get(i - 2);
List<Integer> newLine = new ArrayList<Integer>();
newLine.add(1);
for (int j = 0; j < preLine.size() - 1; j++){
newLine.add(preLine.get(j) + preLine.get(j + 1));
}
newLine.add(1);
res.add(newLine);
}
return res;
}
}
|