LeetCode Q240: 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.

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.

Solution:
Start from upper right corner, move down if target is larger, move left if target is smaller. O(m+n) time complexity.

	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;
	while (i < m && j >= 0) {
	if (matrix[i][j] == target)
	return true;
	else if (matrix[i][j] > target) {
	j--;
	} else
	i++;
	}
	return false;
	}
	};

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