leetcode: Search a 2D Matrix II

最新推荐文章于 2020-07-03 09:27:28 发布

martin_liang

最新推荐文章于 2020-07-03 09:27:28 发布

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本文介绍了一种在已排序的二维矩阵中高效查找目标值的算法。通过从右上角开始搜索，利用矩阵特性快速定位目标，实现时间复杂度为O(m+n)。

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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) {
        
        int rows = matrix.size();
        int columns = matrix[0].size();
        
        if (rows == 0 || columns == 0)
            return 0;

        int curRow = 0;
        int curColumn = columns-1;
        
        while (curColumn >=0 && curRow <rows)
        {
            int comparator = matrix[curRow][curColumn];
            if (comparator == target)
                return true;
                
            if (comparator > target)
                curColumn--;
            else
                curRow++;
        }
        
        return false;
    }
};