[LeetCode][JavaScript]Pascal's Triangle II

Pascal's Triangle II

Given an index k, return the kth row of the Pascal's triangle.

For example, given k = 3,
Return

[1,3,3,1]

.

Note:
Could you optimize your algorithm to use only O(k) extra space?

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

要求常数级的空间复杂度。

只维护一行的数据，每次从后往前算（因为每次是当前的值加上前一个的值，从后往前就不会影响结果），最后补上1。

/**
* @param {number} rowIndex
* @return {number[]}
*/
var getRow = function(rowIndex) {
if(rowIndex === 0){
return [1];
}else if(rowIndex === 1){
return [1, 1];
}

var n = rowIndex - 1;
var row = [1, 1];
while(n--){
for(var i = row.length - 1; i >= 1; i--){
row[i] = row[i] + row[i - 1];
}
row.push(1);
}
return row;
};