让我们把它分成几个步骤。
我们知道行是排序的，所以我们可以首先找到包含该项的行。我还将使用for循环而不是while循环，因为for循环更好地模拟了我们正在做的事情。

bool searchMatrix(vector<vector<int>>& matrix, int target) {
    // use descriptive variables names to make the code easier to understand
    size_t rowCount = matrix.size();
    if (rowCount == 0) return false;
    size_t colCount = matrix[0].size();

    for (size_t r = 0; r < rowCount; r++) {
        // We need to check if the target could be in this row.
        // So there are three cases:

        // 1. Target is less than all items in this row
        if (target < matrix[r][0]) return false;

        // 2. Target is greater than all items in this row
        if (target > matrix[r][colCount - 1]) continue;

        // 3. Target is within this row if present
        // TODO
    }
}

现在，我们知道它在哪一行了，我们只需要搜索那一行，这看起来像是学校的家庭作业题，我不想只给予你们完整的答案，所以希望你们能从这里把剩下的填上。
我想补充的一点是，我们可以通过使用“range based for loops”和std：：vector上的一些helpers方法来消除索引，从而使事情变得更简洁：

bool searchMatrix(vector<vector<int>>& matrix, int target) {
    for (const auto& row : matrix) {
        // We need to check if the target could be in this row.
        // So there are three cases:

        // 1. Target is less than all items in this row
        if (target < row.front()) return false;
        
        // 2. Target is greater than all items in this row
        if (target > row.back()) continue;
        
        // 3. Target is within this row if present
        // TODO (can used a range based for loop for this as well)
    }

    return false;
}