Pascal’s Triangle
Leetcode 118. Pascal’s Triangle
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]
]
class Solution {
public:
vector<vector<int>> generate(int numRows) {
vector<vector<int>> res;
for (int i = 0; i < numRows; i++) {
res.push_back(vector<int>(i+1, 1));
for (int j = 1; j < i; j++)
res[i][j] = res[i-1][j-1] + res[i-1][j];
}
return res;
}
};
Leetcode 119. Pascal’s Triangle II
Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.
For example, given the following triangle
[
[2],
[3,4],
[6,5,7],
[4,1,8,3]
]
The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11).
Note: Bonus point if you are able to do this using only O(n) extra space, where n is the total number of rows in the triangle.
class Solution {
public:
vector<int> getRow(int rowIndex) {
vector<int> res(rowIndex + 1);
res[0] = 1;
for (int i = 0; i <= rowIndex; i++)
for (int j = i; j > 0; j--)
res[j] = res[j] + res[j-1];
return res;
}
};