CODE 13. Triangle

版权声明：本文为博主原创文章，转载请注明出处，谢谢!

版权声明：本文为博主原创文章，转载请注明出处：http://blog.jerkybible.com/2013/09/15/2013-09-15-CODE 13 Triangle/

访问原文「CODE 13. Triangle」

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.
For example, given the following triangle

[
     [2],
    [3,4],
   [6,5,7],
  [4,1,8,3]
]

The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 =
11).
Note:
Bonus point if you are able to do this using only O(n)
extra space, where n is
the total number of rows in the triangle.

public int minimumTotal(ArrayList<ArrayList<Integer>> triangle) {
	// Start typing your Java solution below
	// DO NOT write main() function
	if (null == triangle || 0 == triangle.size()) {
		return 0;
	}

	int layerNumer = triangle.size();
	ArrayList<Integer> tmpLengths = new ArrayList<Integer>();
	tmpLengths.add(triangle.get(0).get(0));
	for (int i = 1; i < layerNumer; i++) {
		ArrayList<Integer> layer = triangle.get(i);
		layer.set(0, layer.get(0) + tmpLengths.get(0));
		for (int k = 1; k < layer.size(); k++) {
			if (k == layer.size() - 1) {
				layer.set(k, layer.get(k) + tmpLengths.get(k - 1));
			} else {
				if (tmpLengths.get(k) > tmpLengths.get(k - 1)) {
					layer.set(k, tmpLengths.get(k - 1) + layer.get(k));
				} else {
					layer.set(k, tmpLengths.get(k) + layer.get(k));
				}
			}
		}
		tmpLengths.clear();
		tmpLengths.addAll(layer);
	}
	int min = tmpLengths.get(0);
	for (int i = 1; i < layerNumer; i++) {
		if (tmpLengths.get(i) < min) {
			min = tmpLengths.get(i);
		}
	}
	return min;
}