Leetcode: 74. Search a 2D Matrix

Description

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.

Example

Consider the following matrix:

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

Given target = 3, return true.

思路

从左下角或右上角开始找，大了就往上(下)，小了就往右(左)

代码

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 = m - 1, j = 0;
while(i >= 0 && j < n){
if(matrix[i][j] == target)
return true;
else if(matrix[i][j] > target)
i--;
else j++;
}

return false;
}
};