Given numRows, generate the first numRows of Pascal’s triangle.

For example, given numRows = 5,
Return

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[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

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function generate(numRows) {
       var number = new Array(numRows);
       for(var k=0;k<numRows;k++){
           number[k]=new Array(k+1);
           number[k][0]=1;
           number[k][k]=1;
       }
       for(var m=2;m<numRows;m++){
           for(var n=1;n<m;n++){
               number[m][n]=number[m-1][n-1] +number[m-1][n];
           }
       }
       return number;
   }