PascalTriangleII.java

package Lc119_PascalTriangleII;

import java.util.ArrayList;
import java.util.List;

/**
 * 119. Pascal's Triangle II
 *
 * Given an integer rowIndex, return the rowIndexth (0-indexed) row of the Pascal's triangle.
 *
 * In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:
 *
 * Example 1:
 *
 * Input: rowIndex = 3
 * Output: [1,3,3,1]
 *
 * Example 2:
 *
 * Input: rowIndex = 0
 * Output: [1]
 *
 * Example 3:
 *
 * Input: rowIndex = 1
 * Output: [1,1]
 *
 *
 * Constraints:
 *
 * 0 <= rowIndex <= 33
 */
public class PascalTriangleII {

    /**
     * Solution 1
     * Time complexity : O(rowIndex^2)
     * Space complexity : O(1)
     */
    public List<Integer> getRow(int rowIndex) {
        List<Integer> ans = new ArrayList<>(rowIndex + 1);
        ans.add(1);
        for (int i = 1; i <= rowIndex; i++) {
            ans.add(0);
            for (int j = i; j > 0; j--) {
                ans.set(j, ans.get(j) + ans.get(j - 1));
            }
        }
        return ans;
    }
}