Triangle.java

class Solution {
    public int minimumTotal(List<List<Integer>> triangle) {
        if (triangle == null || triangle.size() == 0) return 0; 
        int n = triangle.size(); 
        int[] arr = new int[n];
        arr[0] = triangle.get(0).get(0); 
        
        for (int i = 1; i < n; i++) {
            List<Integer> row = triangle.get(i);
            
            for (int j = row.size() - 1; j >= 0; j--) {
                if (j == row.size() - 1) {
                    arr[j] = row.get(j) + arr[j - 1]; 
                } else if (j == 0) {
                    arr[j] = arr[0] + row.get(j);
                } else {
                    arr[j] = Math.min(arr[j - 1], arr[j]) + row.get(j);
                }
            }
        }
        
        int min = arr[0]; 
        for (int i = 1; i < n; i++) {
            if (arr[i] < min) {
                min = arr[i]; 
            }
        }
        
        return min; 
    }
}