【leetcode hot 100 240】搜索二维矩阵Ⅱ

解法一：直接查找

class Solution {public boolean searchMatrix(int[][] matrix, int target) {for(int i=0; i<matrix.length; i++){for(int j=0; j<matrix[0].length; j++){if(matrix[i][j]>target){break;}if(matrix[i][j]==target){return true;}}}return false;}
}

解法二：二分查找

class Solution {public boolean searchMatrix(int[][] matrix, int target) {for (int[] row : matrix) {int index = search(row, target);if (index >= 0) {return true;}}return false;}public int search(int[] nums, int target) {int low = 0, high = nums.length - 1;while (low <= high) {int mid = (high - low) / 2 + low;int num = nums[mid];if (num == target) {return mid;} else if (num > target) {high = mid - 1;} else {low = mid + 1;}}return -1;}
}

注意：

• mid = (high - low) / 2 + low

解法三：（Z 字形查找）从右上角开始查找，若matrix[i][j]>target，则列减少；若matrix[i][j]<target，则列增加。

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