Search a 2D Matrix

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.

1.迭代

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

 

2.递归

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