1966B - Rectangle Filling - CodeForces Solution

def helper(n,mat):
    if mat[0][0] == mat[-1][-1]:
        return 1

    if mat[0][-1] == mat[-1][0]:
        return 1

    ele1, ele2 = mat[0][0], mat[-1][0]
    if ele1 == ele2:
        flag = 0
        for i in range(n):
            if mat[i][-1] == ele1:
                flag = 1
                break

        if flag:
            return 1

    ele1, ele2 = mat[0][-1], mat[-1][-1]
    if ele1 == ele2:
        flag = 0
        for i in range(n):
            if mat[i][0] == ele1:
                flag = 1
                break

        if flag:
            return 1

    return 0


for _ in range(int(input())):
    n,m = map(int,input().split())
    mat,tmat = [],[]
    for i in range(n):
        x = input()
        mat.append(x)

    for i in range(m):
        r = []
        for j in range(n):
            r.append(mat[j][i])

        tmat.append(r)

    if n == 1:
        if mat[0][0] == mat[0][-1]:
            print("YES")

        else:
            print("NO")

        continue

    if m == 1:
        if mat[0][0] == mat[-1][0]:
            print("YES")

        else:
            print("NO")

        continue

    if helper(n,mat) or helper(m,tmat):
        print("YES")

    else:
        print("NO")