剑指 Offer 47. 礼物的最大价值

public int maxValue(int[][] grid) {
        //动态规划
        int m = grid.length;
        int n = grid[0].length;
        for(int i = 1;i<n;i++){
            grid[0][i] = grid[0][i] + grid[0][i-1];
        }
        for(int i = 1;i<m;i++){
            grid[i][0] = grid[i][0] + grid[i-1][0];
        }
        for(int i = 1;i<m;i++){
            for(int j = 1;j<n;j++){
                grid[i][j] = Math.max(grid[i-1][j],grid[i][j-1]) + grid[i][j];
            }
        }
        return grid[m-1][n-1];
    }

 

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class Solution {
    public int maxValue(int[][] grid) {
        if(grid.length == 0 || grid[0].length == 0){
            return 0;
        }
        int[][] log = new int[grid.length][grid[0].length];
        return dfs_47(grid,log,0,0);
    }

    private int dfs_47(int[][] grid, int[][] log, int row, int col) {
        if(row == grid.length -1  && col == grid[0].length-1){
            return grid[row][col];
        }

        if(row>=grid.length || col>=grid[0].length){
            return 0;
        }
        if(log[row][col] > 0){
            return log[row][col];
        }
        int right =  dfs_47(grid,log,row,col + 1);
        int down = dfs_47(grid,log,row+1,col);
        int max = Math.max(right,down) + grid[row][col];
        log[row][col] = max;
        return max;
    }
}