240

240. Search a 2D Matrix II (Medium)

Write an efficient algorithm that searches for a value target in an m x n integer matrix 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 1:

Input: 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]], target = 5
Output: true

Example 2:

Input: 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]], target = 20
Output: false

 

Constraints:

• m == matrix.length
• n == matrix[i].length
• 1 <= n, m <= 300
• -109 <= matrix[i][j] <= 109
• All the integers in each row are sorted in ascending order.
• All the integers in each column are sorted in ascending order.
• -109 <= target <= 109

Related Topics:
Array, Binary Search, Divide and Conquer, Matrix

Similar Questions:

• Search a 2D Matrix (Medium)

Solution 1.

// OJ: https://leetcode.com/problems/search-a-2d-matrix-ii/
// Author: github.com/lzl124631x
// Time: O(M + N)
// Space: O(1)
class Solution {
public:
    bool searchMatrix(vector<vector<int>>& A, int target) {
        int M = A.size(), N = A[0].size(), i = 0, j = N - 1;
        while (i < M && j >= 0) {
            if (A[i][j] == target) return true;
            if (A[i][j] < target) ++i; 
            else --j;
        }
        return false;
    }
};