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  • LeetCode_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.
    

      分析:This problem is more likely to be a (dynamic programming) DP problem,
    where a[n][i] = a[n][i]+min(a[n-1][i], a[n-1][i-1]).
    Note that in this problem, "adjacent" of a[i][j] means a[i-1][j] and a[i-1][j-1], if available(not out of bound), while a[i-1][j+1] is not "adjacent" element.

    The minimum of the last line after computing is the final result.

    class Solution {
    public:
        int minimumTotal(vector<vector<int> > &triangle) {
            // Start typing your C/C++ solution below
            // DO NOT write int main() function
            int len = triangle.size();
            for( int i = 1; i< len ; i++)
              for( int j = 0; j < triangle[i].size(); j++){
                if(j == 0){
                    triangle[i][j] += triangle[i-1][j];
                    continue;
                }
                if(j == triangle[i].size() -1){
                    triangle[i][j] += triangle[i-1][j-1];
                    continue;
                }
                int val = triangle[i-1][j] < triangle[i-1][j-1] ? triangle[i-1][j] 
                                                :triangle[i-1][j-1] ;
               triangle[i][j] += val;
              }
              
            int minval = triangle[len-1][0];
            
            for(int i = 1 ; i< triangle[len-1].size() ; i++){
                if(minval > triangle[len-1][i] ) minval = triangle[len-1][i];
            }
            
            return minval;
        }
    };

    reference :http://yucoding.blogspot.com/2013/04/leetcode-question-112-triangle.html

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  • 原文地址:https://www.cnblogs.com/graph/p/3251518.html
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