leetcode Searcha2DMatrixII
z
 2019-04-09 10:36:27   
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public class Searcha2DMatrixII {
    /**
     * 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.
     * 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]
     * ]
     * [
     * [3, 5,  9,  9, 14],
     * [7, 8, 11, 15, 15],
     * [8,10, 16, 16, 17]]
     * 12
     * Given target = 5, return true.
     *
     * Given target = 20, return false.
     */
    public boolean searchMatrix(int[][] matrix, int target) {
        int lx = 0;
        int ly = 0;
        int rx = matrix[0].length-1;
        int ry = matrix.length-1;
        while (lx < rx && ly < ry) {
            int midx = (lx + rx) / 2;
            int midy = (ly + ry) / 2;
            if ( matrix[midx][midy] == target) return true;
            else if (matrix[midx][midy] < target) {
                lx = midx + 1;
                ly = midy + 1;
            }
            else {
                rx = midx;
                ry = midy;
            }
        }

        int l = 0;
        int r = lx;
        while (l <= r) {
            int mid = (l + r) / 2;
            if (matrix[ly][mid] == target) return true;
            else if (matrix[ly][mid] < target) l = mid + 1;
            else r = mid - 1;
        }

        l = 0;
        r = ly;
        while (l <= r) {
            int mid = (l + r) /2;
            if (matrix[mid][lx] == target) return true;
            if (matrix[mid][lx] < target) l = mid + 1;
            else r = mid - 1;
        }

        return false;
    }
}