[LeetCode] 74. 搜索二维矩阵 ☆☆☆(二分查找)

public static boolean searchMatrix(int[][] matrix, int target) {
        if (null == matrix || matrix.length <= 0 || matrix[0].length <= 0) {
            return false;
        }
        int length = matrix.length;
        int[] lastCol = new int[length];//最后一列
        for (int i = 0; i < length; i++) {
            lastCol[i] = matrix[i][matrix[0].length - 1];
        }
        int lastColIndex = firstLargeIndex(lastCol, target);
        if (lastColIndex == -1) {
            return false;
        }
        //简单二分
        int[] ponitRow = matrix[lastColIndex];//确定了仅可能在这一行
        int start = 0;
        int end = ponitRow.length - 1;
        while (start <= end) {
            int mid = (start + end) >>> 1;
            if (ponitRow[mid] == target) {
                return true;
            } else if (ponitRow[mid] < target) {
                start = mid + 1;
            } else {
                end  = mid - 1;
            }
        }
        return false;
    }

    /**
     * 找第一个 >=target的元素位置
     * @param nums
     * @param target
     * @return
     */
    public static int firstLargeIndex(int[] nums, int target) {
        int start = 0;
        int end = nums.length - 1;
        while (start <= end) {
            int mid = (start + end) >>> 1;
            if (nums[mid] < target) {
                start = mid + 1;
            } else {
                end = mid - 1;
            }
        }
        if (start >= 0 && start <= nums.length - 1) {
            return start;
        }
        return -1;
    }