[leetcode] 417. Pacific Atlantic Water Flow

[leetcode] 417. Pacific Atlantic Water Flow

Description

Given an m x n matrix of non-negative integers representing the height of each unit cell in a continent, the “Pacific ocean” touches the left and top edges of the matrix and the “Atlantic ocean” touches the right and bottom edges.

Water can only flow in four directions (up, down, left, or right) from a cell to another one with height equal or lower.

Find the list of grid coordinates where water can flow to both the Pacific and Atlantic ocean.

Note:

The order of returned grid coordinates does not matter.Both m and n are less than 150.Example:

Given the following 5x5 matrix: Pacific ~ ~ ~ ~ ~ ~ 1 2 2 3 (5) * ~ 3 2 3 (4) (4) * ~ 2 4 (5) 3 1 * ~ (6) (7) 1 4 5 * ~ (5) 1 1 2 4 * * * * * * AtlanticReturn:[[0, 4], [1, 3], [1, 4], [2, 2], [3, 0], [3, 1], [4, 0]] (positions with parentheses in above matrix).

分析

题目的意思是：给定一个m*n的矩阵，左上角是太平洋，右下角是大西洋，找出既能够到太平洋又能到大西洋的坐标。

从边缘当作起点开始遍历搜索，然后标记能到达的点位true，分别标记出pacific和atlantic能到达的点，那么最终能返回的点就是二者均为true的点。我们可以先用DFS来遍历二维数组.

代码

class Solution {private: vector> dirs={{-1,0},{1,0},{0,-1},{0,1}};public: vector> pacificAtlantic(vector>& matrix) { if(matrix.empty()) return {}; vector> res; int m=matrix.size(); int n=matrix[0].size(); vector> pacific(m,vector(n,false)); vector> atlantic(m,vector(n,false)); for(int i=0;i>& matrix,vector>& visited,int pre,int i,int j){ int m=matrix.size(); int n=matrix[0].size(); if(i<0||i>=m||j<0||j>=n||visited[i][j]||matrix[i][j]

参考文献

​​[LeetCode] Pacific Atlantic Water Flow 太平洋大西洋水流​​

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