General Bug Summary

• char doesn't have empty one, which means there is no expression like:

char c = '';

• Binary Search question: definitely make sure the return value is the index or the value on the position. *[Binary Search] should assign mid idx to left, right, rather than assign left or right idx to mid;

// Right way:
if (array[mid] < target) {
    left = mid;
} else {
    right = mid;
}

// Wrong way:
if (array[mid] < target) {
    mid = left;
} else {
    mid = right;
}