LeetCode 63. Minimum Path Sum
2014-07-06 12:08
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一开始写了个用最小堆维护的dijkstra, 想可能是最短路问题。
直到有次expected 82, output 79时,就明白了题目未说明的约束条件:只能向右或向下移动。真是坑。
于是问题变成了基础DP: sum[i][j] = min(sum[i-1][j], sum[i][j-1]) + grid[i][j].
代码:
直到有次expected 82, output 79时,就明白了题目未说明的约束条件:只能向右或向下移动。真是坑。
于是问题变成了基础DP: sum[i][j] = min(sum[i-1][j], sum[i][j-1]) + grid[i][j].
代码:
class Solution { public: int minPathSum(vector<vector<int> > &grid) { if (grid.size() == 0) { return 0; } // trick, 变成(n+1)*(m+1)矩阵, 避免了边界的初始化问题. vector<vector<int>> sum(grid.size()+1, vector<int>(grid[0].size()+1, INT_MAX)); for (int i = 1; i < sum.size(); ++ i) { for (int j = 1; j < sum[0].size(); ++ j) { if (i==1 && j==1) { sum[1][1] = grid[0][0]; } else { sum[i][j] = min(sum[i-1][j], sum[i][j-1]) + grid[i-1][j-1]; } } } return sum[sum.size()-1][sum[0].size()-1]; } };
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