240. 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.

一刷
题解：因为每一行左<右，每一列，上<下
所以从右上角开始寻找。如果小于target就向下，如果大于target就向左

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if(matrix == null || matrix.length==0 || matrix[0].length == 0) return false;
        int col = matrix[0].length-1;
        int row = 0;
        while(col>=0 && row<=matrix.length-1){
            if(target == matrix[row][col]) return true;
            else if(target

二刷
同上

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if(matrix.length == 0) return false;
        int m = matrix.length;
        int n = matrix[0].length;
        int row = 0, col = n-1;
        while(row=0){
            if(matrix[row][col]>target) col--;
            else if(matrix[row][col]

Binary Search