Minimum Path Sum

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.

public class Solution {
    public int minPathSum(int[][] grid) {
        int len1 = grid.length;
        if(len1==0) return 0;
        int len2 = grid[0].length;
        int []dp = new int [len2];
        dp[0] = 0;
        for(int i=0;i<len1;i++){
            for(int j=0;j<len2;j++){
                if(j==0){
                    dp[j] = dp[j]+grid[i][0];
                }
                else if(i==0){
                    dp[j] = dp[j-1]+grid[0][j];
                }
                else {
                    dp[j] = Math.min(dp[j],dp[j-1])+grid[i][j];
                }
            }
        }
        return dp[len2-1];
    }
}