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PascalsTriangleII.java

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/**

* 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?

*/

import java.util.ArrayList;

public class PascalsTriangleII {

public ArrayList<Integer> getRow(int rowIndex) {

ArrayList<Integer> ret = new ArrayList<Integer>();

int[] tmp = new int[rowIndex + 1];

for (int i = 0; i <= rowIndex; i++) {

ret.add(1);

tmp[i] = 1;

}

for (int k = 2; k <= rowIndex; k++) {

int mid = k / 2;

for (int i = 1; i <= mid; i++) {

ret.set(i, tmp[i - 1] + tmp[i]);

}

for (int m = k; m > mid; m--) {

ret.set(m, ret.get(k - m));

}

for (int n = 0; n <= k; n++) {

tmp[n] = ret.get(n);

}

}

return ret;

}

}