【LeetCode】120. Triangle

120. Triangle

Medium

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.

注意点：

1. 转移状态方程。

2. 可以在原二维vector上操作。

3. 注意题意，取最后一排最小值。

int minimumTotal(vector<vector<int> >& triangle) {
    if(triangle.empty()) return 0;
    int i,j; int ans = INT_MAX;
    if(1==triangle.size()) return triangle[0][0];
    for(i=1;i<triangle.size();i++){
    	for(j=0;j<triangle[i].size();j++){
    		if(j==0) 
				triangle[i][j]=triangle[i-1][j]+triangle[i][j];
    		else if(j==triangle[i].size()-1) 
				triangle[i][j]=triangle[i-1][j-1]+triangle[i][j];
    		else 
				triangle[i][j]=min(triangle[i-1][j-1],triangle[i-1][j])+triangle[i][j];
		}
	}
	int row = triangle.size()-1;
	for(int k=0;k<triangle[row].size();k++){
		ans = ans<triangle[row][k]?ans:triangle[row][k];
	}
	return ans;
}