leetcode 240. Search a 2D Matrix II

Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:

Integers in each row are sorted in ascending from left to right.

Integers in each column are sorted in ascending from top to bottom.

For example,

Consider the following matrix:

[

  [1,   4,  7, 11, 15],

  [2,   5,  8, 12, 19],

  [3,   6,  9, 16, 22],

  [10, 13, 14, 17, 24],

  [18, 21, 23, 26, 30]

]

Given target = 5, return true.

Given target = 20, return false.

class Solution {
public:
bool searchMatrix(vector<vector<int>>& matrix, int target) {
if(matrix.empty())
return false;
if(matrix[0].empty())
return false;
if(matrix[0][0]>target||matrix[matrix.size()-1][matrix[0].size()-1]<target)
return false;
int curX=0,curY=0;
bool horizontal=true;
while(curX!=matrix[0].size()&&curY!=matrix.size())
{
if(horizontal)
{
while(curX!=matrix[0].size()&&matrix[curY][curX]<target)
curX++;
if(curX==matrix[0].size()||matrix[curY][curX]>target)
{
curX--;
horizontal=false;
curY++;
}
else
return true;
}
else
{
while(curY!=matrix.size()&&matrix[curY][curX]<target)
curY++;
if(curY==matrix.size()||matrix[curY][curX]>target)
{
if(curY==matrix.size()&&matrix[curY-1][curX]<target)
return false;
curY--;
horizontal=false;
curX--;
}
else
return true;
}
}
return false;
}
};

accepted