Problem:
Score : 900 points

Problem Statement

You are given an undirected graph consisting of N vertices and M edges.
The vertices are numbered 1 to N, and the edges are numbered 1 to M.
In addition, each vertex has a label, A or B. The label of Vertex i is s_i.
Edge i bidirectionally connects vertex a_i and b_i.

The phantom thief Nusook likes to choose some vertex as the startpoint and traverse an edge zero or more times.
Today, he will make a string after traveling as above, by placing the labels of the visited vertices in the order visited, beginning from the startpoint.

For example, in a graph where Vertex 1 has the label A and Vertex 2 has the label B, if Nusook travels along the path 1 \rightarrow 2 \rightarrow 1 \rightarrow 2 \rightarrow 2, the resulting string is ABABB.

Determine if Nusook can make all strings consisting of A and B.

Constraints

2 \leq N \leq 2 \times 10^{5}

1 \leq M \leq 2 \times 10^{5}

|s| = N

s_i is A or B.

1 \leq a_i, b_i \leq N

The given graph may NOT be simple or connected.

Input

Input is given from Standard Input in the following format:

N M
s
a_1 b_1
:
a_{M} b_{M}

Output

If Nusook can make all strings consisting of A and B, print Yes; otherwise, print No.

Sample Input 1

2 3
AB
1 1
1 2
2 2

Sample Output 1

Yes

Since Nusook can visit Vertex 1 and Vertex 2 in any way he likes, he can make all strings consisting of A and B.

Sample Input 2

4 3
ABAB
1 2
2 3
3 1

Sample Output 2

No

For example, Nusook cannot make BB.

The given graph may not be connected.

Sample Input 3

13 23
ABAAAABBBBAAB
7 1
10 6
1 11
2 10
2 8
2 11
11 12
8 3
7 12
11 2
13 13
11 9
4 1
9 7
9 6
8 13
8 6
4 10
8 7
4 3
2 1
8 12
6 9

Sample Output 3

Yes

Sample Input 4

13 17
BBABBBAABABBA
7 1
7 9
11 12
3 9
11 9
2 1
11 5
12 11
10 8
1 11
1 8
7 7
9 10
8 8
8 12
6 2
13 11

Sample Output 4

No

Solution in Go (1.6) (judge verdict: Accepted)

package main

import (
  "bufio"
  "os"
  "strconv"
  "strings"
  "fmt"
)

var reader = bufio.NewReaderSize(os.Stdin, 1000000)
var writer = bufio.NewWriter(os.Stdout)
func NextLine() string {
  buffer := make([]byte, 0)
  for true {
    line, isPrefix, err := reader.ReadLine()
    if err != nil { panic(err) }
    buffer = append(buffer, line...)
    if !isPrefix { break }
  }
  return string(buffer)
}
func NextInt() int {
  n, _ := strconv.Atoi(NextLine())
  return n
}
func NextIntVec() []int {
  L := strings.Split(NextLine(), " ")
  N := make([]int, len(L))
  for i := range N {
    N[i], _ = strconv.Atoi(L[i])
  }
  return N
}
func Write(s interface{}) {
  fmt.Fprintln(writer, s)
}
func Output() {
  _ = writer.Flush()
}

func Solve() {
  NM := NextIntVec()
  N, M := NM[0], NM[1]
  V := make([]int, N)
  G := make([][]int, N)
  for i := range G {
    G[i] = make([]int, 0)
  }
  S := NextLine()
  for i, s := range S {
    V[i] = int(s - rune('A'))
  }
  D := make([][]int, N)
  for i := range D {
    D[i] = make([]int, 2)
  }
  for i := 0; i < M; i++ {
    AB := NextIntVec()
    a, b := AB[0] - 1, AB[1] - 1
    G[a] = append(G[a], b)
    G[b] = append(G[b], a)
    D[a][V[b]]++
    D[b][V[a]]++
  }
  Q := make([]int, 0)
  for i, d := range D {
    if d[0] < 1 || d[1] < 1 {
      Q = append(Q, i)
    }
  }
  for 0 < len(Q) {
    q := Q[0]
    Q = Q[1:]
    for _, adj := range G[q] {
      if D[adj][0] < 1 || D[adj][1] < 1 { continue }
      D[adj][V[q]]--
      if D[adj][V[q]] < 1 { Q = append(Q, adj) }
    }
  }
  for _, d := range D {
    if 0 < d[0] && 0 < d[1] {
      Write("Yes")
      return
    }
  }
  Write("No")
  return
}

func main() {
  Solve()
  Output()
}