leetcode 64 Minimum Path Sum
z
 2018-03-05 10:11:32  

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.

Note: You can only move either down or right at any point in time.

Example 1:

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[[1,3,1],
 [1,5,1],
 [4,2,1]]

Given the above grid map, return 

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7

. Because the path 1→3→1→1→1 minimizes the sum.

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class Solution {
    public int minPathSum(int[][] grid) {
        if(grid == null || grid.length == 0) return 0;
        int m = grid.length;
        int n = grid[0].length;
        int sum = 0;
        int[][] dp = new int[m][n];
        for(int i=0; i<m; i++){
            for(int j=0; j<n; j++){
                if(i==0 && j==0)
                    dp[i][j] =grid[0][0];
                else if(i == 0){
                    dp[i][j] = dp[i][j-1] + grid[i][j];
                }
                else if(j==0){
                    dp[i][j] = dp[i-1][j] + grid[i][j];
                }
                else{
                    dp[i][j] = Math.min(dp[i-1][j], dp[i][j-1]) + grid[i][j];
                }
            }    
        }
        return dp[m-1][n-1];
        
    }
}
  • 这种情况下，不需要使用DP数组。使用DP数组的好处就是能够不改变Grid中的内容。