[leetcode 118] Pascal's Triangle

Given a non-negative integer numRows, generate the first numRows of Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it.

Example:

Input: 5 Output: [ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1] ]

 

문제 풀이

난이도 easy

dp로 구현하면 되는 문제이다. 자바로 구현방법 익히기!!!

class Solution {
    public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> tr = new ArrayList<List<Integer>>();
        
        if(numRows == 0){
            return tr;
        }
        
        tr.add(new ArrayList<>());
        tr.get(0).add(1);
        
        for(int i=1; i<numRows; i++){
            List<Integer> row = new ArrayList<>();
            List<Integer> prev = tr.get(i-1);
            
            row.add(1);
            
            for(int j=1; j<i; j++){
               row.add(prev.get(j-1) + prev.get(j)); 
            }
            row.add(1);
            tr.add(row);
        }
        
        return tr;
    }
}

 

아래는 c이다.

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        
        vector<vector<int>> result;
        if(numRows == 0){
            return result;
        }
        
        result.push_back({1});

        if(numRows == 1){
            return result;
        }
        
        result.push_back({1,1});
        if(numRows == 2){
            return result;
        }
        
        for(int i = 3; i<=numRows; i++){
            
            vector<int> cur(i,0);
            result.push_back(cur);
            
            result[i-1][0] = result[i-1][i-1] = 1;
            for(int j=1; j<i-1; j++){
                result[i-1][j] = result[i-2][j] + result[i-2][j-1];
            }
        }
        
        return result;
    }
};