Leetcode Yanghui triangle

My solution ： Each number of the next layer is the sum of the upper left and upper right of the layer

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        class Solution {
        
    public List<List<Integer>> generate(int numRows) {
        
        List<List<Integer>> outter=new ArrayList<List<Integer>>();
        
        if(numRows==0)
        
            return outter;
        
        ArrayList<Integer> inner = new ArrayList<Integer>();
        
        inner.add(1);
        
        outter.add(inner);
        
        int outterIndex=0;
        
        while(outter.size()!=numRows) {
        
            ArrayList<Integer> lastLevel = (ArrayList<Integer>) outter.get(outterIndex);
        
            ArrayList<Integer> tmp = new ArrayList<Integer>();
        
            for(int i=0;i<lastLevel.size()+1;i++) {
        
                int left=i>0?lastLevel.get(i-1):0;
        
                int right=i<lastLevel.size()?lastLevel.get(i):0;
        
                int res=left+right;
        
                tmp.add(res);
        
            }
        
            outter.add(tmp);
        
            outterIndex++;
        
        }
        
        return outter;
        
    }
        
}
       
       

        
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