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  • 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.
    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.

    Approach #1 Using binary search in each column.

    ```CPP class Solution { public: bool searchMatrix(vector>& matrix, int target) { int len1 = matrix.size(); if (len1 == 0) return false; int len2 = matrix[0].size(); if (len2 == 0) return false; for (int i = 0; i < len1; ++i) { auto it = lower_bound(matrix[i].begin(), matrix[i].end(), target); if (it < matrix[i].end() && *it == target) return true; } return false; } };
    </font>
    Runtime: 88 ms, faster than 23.74% of C++ online submissions for Search a 2D Matrix II.
    
    
    #### Approach #2  
    ```CPP
    class Solution {
    public:
        bool searchMatrix(vector<vector<int>>& matrix, int target) {
            int m = matrix.size();
            if (m == 0) return false;
            int n = matrix[0].size();
            int i = 0, j = n - 1;
            for (; i < m && j >= 0; ) {
                if (matrix[i][j] == target) return true;
                else if (matrix[i][j] > target) j--;
                else i++;
            }
            return false;
        }
    };
    

    Runtime: 52 ms, faster than 55.98% of C++ online submissions for Search a 2D Matrix II.

    永远渴望,大智若愚(stay hungry, stay foolish)
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  • 原文地址:https://www.cnblogs.com/h-hkai/p/9900956.html
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