Search a 2D Matrix II

最新推荐文章于 2021-03-02 01:17:16 发布

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本文介绍了一种高效的算法，用于在一个特殊属性的矩阵中搜索特定值。该矩阵的每一行和每一列都按升序排列。算法从矩阵的右上角开始，并根据目标值与当前值的关系调整搜索方向。

题目来源LeetCode

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.

这道题从矩阵的右上角开始，根据行列都是从小到大排列的性质，目标小于矩阵数则列数-1，目标大于矩阵数则行数+1，（这道题遇到的问题是没有考虑矩阵为空，需要判断一下再进行）代码如下：

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