动态规划
var minPathSum = function(grid) {
let m = grid.length,n = grid[0].length;
for(let i=1;i<m;i++)grid[i][0]+=grid[i-1][0];
for(let i=1;i<n;i++)grid[0][i]+=grid[0][i-1];
for(let i=1;i<m;i++){
for(let j=1;j<n;j++){
grid[i][j]+=Math.min(grid[i-1][j],grid[i][j-1]);
}
}
return grid[m-1][n-1];
};