面试10大算法题汇总-字符串和数组9

20.寻找2D矩阵

给定一个从左到右从上到下递增的m*n矩阵，判断target是否在矩阵中

例：

[

[1,  3,  5, 7],

[10, 11, 16, 20],

[23, 30, 34, 50]

]

Target=3

返回：true

思路：二分查找

Code：

public class test {
	public static boolean searchMatrix(int[][] matrix, int target) {
		if (matrix == null || matrix.length == 0 || matrix[0].length == 0)
			return false;

		int m = matrix.length;
		int n = matrix[0].length;

		int begin = 0;
		int end = m * n - 1;
		while (begin < end) {
			int mid = (begin + end) / 2;
			int midX = mid / n;
			int midY = mid % n;

			if (matrix[midX][midY] == target)
				return true;
			if (matrix[midX][midY] < target) {
				begin = mid + 1;
			} else {
				end = mid - 1;
			}
		}
		return false;
	}

	public static void main(String[] args) {
		int[][] arr = { { 1, 3, 5, 7 }, { 10, 11, 16, 20 }, { 23, 30, 34, 50 } };
		System.out.println(searchMatrix(arr, 3));
	}
}