240. Search a 2D Matrix II

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240. Search a 2D Matrix II

Description

Difficulty: Medium

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

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:

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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:

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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

Hints/Notes

  • start from top right corner

Solution

Language: C++

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