74. Search a 2D Matrix

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

        return false;
    }
}
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class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int m = matrix.length, n = matrix[0].length;

        int i = 0, j = m * n - 1;
        while (i <= j) {
            int mid = (i + j) >> 1;
            int midVal = matrix[mid / n][mid % n]; // 注意定位行和列的索引都是对 n 计算
            if (target < midVal) {
                j = mid - 1; // 目标值小于中点值，缩小范围至左侧区间继续搜索
            } else if (target > midVal) {
                i = mid + 1; // 目标值大于中点值，缩小范围至右侧区间继续搜索
            } else {
                return true;
            }
        }

        return false;
    }
}

References

74. Search a 2D Matrix