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| #include<bits/stdc++.h>
#define ll long long
#define INF 2147483647
#define lc(a) ((a) << 1)
#define rc(a) ((a) << 1 | 1)
int inp(){
char c = getchar();
while(c < '0' || c > '9')
c = getchar();
int sum = 0;
while(c >= '0' && c <= '9'){
sum = sum * 10 + c - '0';
c = getchar();
}
return sum;
}
struct SEG{
int l;
int r;
int sum[30];
int lazy;
void clear(){
memset(sum, 0, sizeof(sum));
}
};
int cnt[30];
char s[100010];
SEG operator + (SEG a, SEG b){
if(a.l == -1)
return b;
if(b.l == -1)
return a;
SEG ret;
ret.l = a.l;
ret.r = b.r;
for(int i = 0; i < 26; i++)
ret.sum[i] = a.sum[i] + b.sum[i];
return ret;
}
struct SEG_Tree{
SEG t[800010];
void push_up(int cur){
for(int i = 0; i < 26; i++)
t[cur].sum[i] = t[lc(cur)].sum[i] + t[rc(cur)].sum[i];
}
void build(int cur, int l, int r){
t[cur].lazy = -1;
t[cur].l = l;
t[cur].r = r;
if(l == r){
t[cur].clear();
t[cur].sum[s[l] - 'a'] = 1;
return ;
}
int mid = (l + r) >> 1;
build(lc(cur), l, mid);
build(rc(cur), mid + 1, r);
push_up(cur);
}
void push_down(int cur){
if(t[cur].lazy != -1){
t[lc(cur)].clear();
t[rc(cur)].clear();
t[lc(cur)].sum[t[cur].lazy] = t[lc(cur)].r - t[lc(cur)].l + 1;
t[rc(cur)].sum[t[cur].lazy] = t[rc(cur)].r - t[rc(cur)].l + 1;
t[lc(cur)].lazy = t[rc(cur)].lazy = t[cur].lazy;
}
t[cur].lazy = -1;
}
void query(int cur, int l, int r){
SEG nul;
nul.l = -1;
if(t[cur].l > r || t[cur].r < l)
return ;
push_down(cur);
if(t[cur].l >= l && t[cur].r <= r){
for(int i = 0; i < 26; i++)
cnt[i] += t[cur].sum[i];
return ;
}
query(lc(cur), l, r);
query(rc(cur), l, r);
}
void modify(int cur, int l, int r, int c){
if(t[cur].l > r || t[cur].r < l)
return ;
if(t[cur].l >= l && t[cur].r <= r){
t[cur].clear();
t[cur].sum[c] = t[cur].r - t[cur].l + 1;
t[cur].lazy = c;
return ;
}
push_down(cur);
modify(lc(cur), l, r, c);
modify(rc(cur), l, r, c);
push_up(cur);
}
void print(int cur){
if(t[cur].l == t[cur].r){
for(int i = 0; i < 26; i++)
if(t[cur].sum[i])
putchar('a' + i);
return ;
}
push_down(cur);
print(lc(cur));
print(rc(cur));
}
}t;
int main(){
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
int n = inp();
int q = inp();
scanf("%s", s + 1);
t.build(1, 1, n);
while(q--){
int l = inp();
int r = inp();
memset(cnt, 0, sizeof(cnt));
t.query(1, l, r);
if((r - l + 1) & 1){
int cs = 0, num;
for(int i = 0; i < 26; i++)
if(cnt[i] & 1){
cs++;
num = i;
}
if(cs == 1){
int mid = (l + r) >> 1;
t.modify(1, mid, mid, num);
int cc = 0;
for(int i = 0; i < 26; i++){
if(cnt[i] <= 1)
continue;
int c2 = cc + (cnt[i] >> 1);
t.modify(1, l + cc, l + c2 - 1, i);
t.modify(1, r - c2 + 1, r - cc, i);
cc = c2;
}
}
} else {
int cs = 0, num = -1;
for(int i = 0; i < 26; i++)
if(cnt[i] & 1){
cs++;
num = i;
}
if(cs == 0){
int cc = 0;
for(int i = 0; i < 26; i++){
if(cnt[i] == 0)
continue;
int c2 = cc + (cnt[i] >> 1);
t.modify(1, l + cc, l + c2 - 1, i);
t.modify(1, r - c2 + 1, r - cc, i);
cc = c2;
}
}
}
}
t.print(1);
putchar('\n');
}
|
