240. Search a 2D Matrix II && 74. 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 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.

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

注意while里面的i判断为》=0而不是》0！！！！

74.

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.

代码也同上~