SodhanaLibrary

function generate(numRows) {
    var result = [];
    if (numRows <= 0)
           return result;
 
    var pre = [];
    pre.push(1);
    result.push(pre);
 
    for (var i = 2; i <= numRows; i++) {
        var cur = [];
 
        cur.push(1); //first
        for (var j = 0; j < pre.length - 1; j++) {
            cur.push(pre[j] + pre[j + 1]); //middle
        }
        cur.push(1);//last
 
        result.push(cur);
        pre = cur;
    }
    return result;
}