[LeetCode] 095: Search a 2D Matrix

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本文介绍了一种高效的矩阵搜索算法，该算法能在排序矩阵中快速查找指定数值。矩阵特性为每行从左到右递增排序，且每行首个元素大于前一行末尾元素。通过实例演示了如何使用该算法。

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[Problem]

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 from left to right.
The first integer of each row is greater than the last integer of the previous row.

For example,

Consider the following matrix:

[
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]

Given target = 3, return true.

[Solution]

class Solution {
public:
	bool searchMatrix(vector<vector<int> > &matrix, int target) {
		// Note: The Solution object is instantiated only once and is reused by each test case.
		int m = matrix.size();
		if(m <= 0)return false;
		int n = matrix[0].size();

		// search
		bool res = false;
		int i = 0, j = n-1;
		while(i < m && j >= 0){
			if(target > matrix[i][j]){
				i++;
			}
			else if(target < matrix[i][j]){
				j--;
			}
			else{
				res = true;
				break;
			}
		}
		return res;
	}
};