118. Pascal's Triangle

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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:

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


一會看下被人的code 
Dp 

https://leetcode.com/problems/pascals-triangle/solution/

class Solution {
    public List<List<Integer>> generate(int numRows) {
        int n = numRows;
        int[][] res = new int[n][n];
        // fill in the base case 
    // fill in the first and the last on each row with 1 
        for(int i = 0; i < n; i++){
            // row is I, col is 0, and I 
            res[i][0] = 1;
            res[i][i] = 1;
        }
        // induction rule 
    // current = top + top left 
    // top has the same col, row - 1 
    // top left is row - 1, col - 1 
    // start from the third row, always start from the second col, ending at the last col - 1 
    // last col is I 
        for(int r = 2; r < n; r++){
            for(int c = 1; c < n - 1; c++){
                res[r][c] = res[r - 1][c - 1] + res[r - 1][c];
            }
        }
        List<List<Integer>> result = new ArrayList<>();
        for(int i = 0; i < res.length; i++){
            List<Integer> tmp = new ArrayList<>();
            for(int j = 0; j < res[i].length; j++){
                if(res[i][j] != 0){
                    tmp.add(res[i][j]);
                }
            }
            result.add(new ArrayList<>(tmp));
        }
        return result;
        
    }
}


// others concise code , without converting int[][] to list<list<integer>> 
https://leetcode.com/problems/pascals-triangle/discuss/38141/My-concise-solution-in-Java