萌新全wa求大佬看看哪里错了

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<iostream>
#include<queue>
using namespace std;

typedef long long ll;
const int N = 200010;

int n, m;
char c[N];
int a[N], b[N], vis[N];
struct node {
	int val, l, r;
	bool operator < (const node& b) const {
		if(val == b.val) {
			if(l == b.l) return b.r < r;
			return b.l < l;
		}
		return b.val < val;
	}
};
priority_queue<node> q;

int main () {
	//freopen("dancinglessons.in", "r", stdin);
	//freopen("dancinglessons.out", "w", stdout);
	scanf("%d", &n);
	int x = 0, y = 0;
	for(int i = 1; i <= n; i ++ ) {
		cin >> c[i];
		if(c[i] == 'B') x ++ , b[i] = 1;
		if(c[i] == 'G') y ++ , b[i] = 0;
	}
	//for(int i = 1; i <= n; i ++ ) cout << b[i] << " ";
	m = min(x, y);
	for(int i = 1; i <= n; i ++ ) scanf("%d", &a[i]);
	for(int i = 1; i < n; i ++ ) {
		if(b[i] + b[i + 1] == 1) {
			node x = {abs(a[i] - a[i + 1]), i, i + 1};
			q.push(x);
		}
	}
	printf("%d", m);
	while(!q.empty()) {
		node k = q.top();
		q.pop();
		if(!vis[k.l] && !vis[k.r]) {
			vis[k.l] = vis[k.r] = 1;
			printf("\n%d %d", k.l, k.r);
			if(k.l - 1 >= 1 && k.r + 1 <= n && b[k.l - 1] + b[k.r + 1] == 1) {
				node x = {abs(a[k.l - 1] - a[k.r + 1]), k.l - 1, k.r + 1};
				q.push(x);
			}
		}
	}
	//fclose(stdin);
	//fclose(stdout);
	return 0;
}