leetcode 118. Pascal's Triangle

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.

 

 

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

 

 

var generate = function(numRows) {
    var ans = [];
    for(var i=0;i<numRows;i++){
        if(i===0){
            ans[i]=[1];
            continue;
        }
        ans[i] = [];
        for(var j=0;j<=i;j++){
            if(j===0){
                ans[i][j] = ans[i-1][j];
            }else if(j===i){
                ans[i][j] = ans[i-1][j-1];
            }else{
                ans[i][j] = ans[i-1][j-1] + ans[i-1][j]
            }
        }
    }
    return ans; 
};