Leetcode 240. Search a 2D Matrix II

Topic:

Write an efficient algorithm, searches for a value in a m x n Matrix. This matrix has the following properties:

• Integers in each row is sorted in ascending from left to right.
• Integers in each column is sorted in ascending from top to bottom.

For example,

Consider the following matrix:

[  [1,   4,  7, one, a],  [2,   5, 8,, +  ],  [3,   6,  9, +, +],  [10, 13, 14, 17,  [18, 21, 23, 26, 30]

Given target = 5 , return true .

Given target = 20 , return false .

Ideas:

1. Two points find the first column to find the highest row, two to find the last column to find the lowest row, and then pair each row with two points to find O (M * lgn)

2. Two-point search for each line directly O (M * lgn)

3. For each number, the top is smaller than it, the right is larger than it O (M * N)

Code C + + idea 2:

BOOLBin_search (vector<int>& num,inttarget) {    intStart =0; intEnd = Num.size ()-1;  while(Start <=end) {        intMID = start + (End-start)/2; if(Num[mid] = =target)return true; Else if(Num[mid] >target) End= Mid-1; Else if(Num[mid] <target) Start= Mid +1; }    return false;}classSolution { Public:    BOOLSearchmatrix (vector<vector<int>>& Matrix,inttarget) {         for(inti =0; I <= matrix.size ()-1; i++) {            if(Bin_search (matrix[i],target))return true; }        return false; }};

Leetcode 240. Search a 2D Matrix II