def findNotZeroIndex(a, fromIdx):
    """ ([[int]], int) => int
        Look up not zero item from a[fromIdx][fromIdx]
        to a[len(a)][fromIdx].
        if found return index
        if did not find return -1
    """
    n = len(a)
    for i in range(fromIdx+1,n):
        if a[i][fromIdx] != 0:
            return i
    return -1