leetcode 240. Search a 2D Matrix II-蒲公英云

leetcode 240. Search a 2D Matrix II

冷不防 2022-08-20 14:07 206阅读 0赞

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;
    }
};