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PascalTriangle.java

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import java.util.ArrayList;

/**

* Given numRows, generate the first numRows of Pascal's triangle.

*

* For example, given numRows = 5, Return

*

* [

* [1],

* [1,1],

* [1,2,1],

* [1,3,3,1],

* [1,4,6,4,1]

* ]

*/

public class PascalTriangle {

public ArrayList<ArrayList<Integer>> pascalTriangle(int numRows) {

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

int k = 1;

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

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

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

r.add(1);

}

k++;

pt.add(r);

}

for (int f = 2; f < pt.size(); f++) {

ArrayList<Integer> prev = pt.get(f - 1);

ArrayList<Integer> current = pt.get(f);

for (int g = 1; g < current.size() - 1; g++) {

current.set(g, prev.get(g - 1) + prev.get(g));

}

}

return pt;

}

}