Lc0980

05 August 2008

980. Unique Paths III

分析

dfs最基础的应用是寻找迷宫是否能走出 这里多了几个约束条件：

分别对上述约束条件进行分析：

代码

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class Solution {
    int result;
    public int uniquePathsIII(int[][] grid) {
        result = 0;
        if (grid == null || grid.length == 0 || grid[0].length == 0) {
            return result;
        }
        int m = grid.length;
        int n = grid[0].length;
        int startx = 0, starty = 0;
        int steps = 1;

        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                if (grid[i][j] == 1) {
                    startx = i;
                    starty = j;
                    continue;
                }
                if (grid[i][j] == 0) {
                    steps++;
                }
            }
        }
        dfs(grid, startx, starty, steps);
        return result;
    }
    private void dfs(int[][] grid, int px, int py, int steps) {
        if (px < 0 || px >= grid.length || py < 0 || py >= grid[0].length || grid[px][py] == -1) {
            return;
        }
        if (grid[px][py] == 2) {
            if (steps == 0) {
                result++;
            }
            return;
        }
        grid[px][py] = -1;
        steps--;
        dfs(grid, px + 1, py, steps);
        dfs(grid, px - 1, py, steps);
        dfs(grid, px, py + 1, steps);
        dfs(grid, px, py - 1, steps);
        grid[px][py] = 0;
    }
}