87 lines
1.5 KiB
Plaintext
87 lines
1.5 KiB
Plaintext
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int quick_read(){
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int ch = getch(); int x = 0, f = 0;
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while (ch < 48 || ch > 57){
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if (ch == 45) f = 1;
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ch = getch();
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}
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while (ch >= 48 && ch <=57){
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x = x * 10 + ch - 48;
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ch = getch();
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}
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if (f) return -x;
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else return x;
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}
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const int maxn = 10005;
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int n, m, f[maxn][20], dep[maxn];
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int to[maxn], next[maxn], head[maxn], cnt = 0;
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void add_edge(int from, int To){
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to[cnt] = To;
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next[cnt] = head[from];
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head[from] = cnt;
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cnt = cnt + 1;
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f[To][0] = from;
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}
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void init(){
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dep[0] = 0x3f3f3f3f;
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int i = 1;
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while (i <= n){
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head[i] = -1;
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i = i + 1;
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}
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}
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void tree(int x, int d){
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dep[x] = d;
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int i = 0;
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while (f[x][i]){
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f[x][i + 1] = f[f[x][i]][i];
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i = i + 1;
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}
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i = head[x];
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while (i != -1){
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int y = to[i];
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tree(y, d + 1);
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i = next[i];
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}
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}
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int LCA(int x, int y){
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if (dep[x] < dep[y]){
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int t = x;
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x = y;
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y = t;
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}
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int i = 19;
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while (dep[x] > dep[y]){
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if (f[x][i] && dep[f[x][i]] >= dep[y])
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x = f[x][i];
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i = i - 1;
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}
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if (x == y) return x;
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i = 19;
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while (i >= 0){
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if (f[x][i] != f[y][i]){
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x = f[x][i];
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y = f[y][i];
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}
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i = i - 1;
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}
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return f[x][0];
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}
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int main(){
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n = quick_read(); m = quick_read();
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init();
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int i = 1;
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while (i != n){
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int x = quick_read(), y = quick_read();
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add_edge(x, y);
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i = i + 1;
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}
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tree(1, 1);
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while (m){
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int x = quick_read(), y = quick_read();
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putint(LCA(x, y));
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putch(10);
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m = m - 1;
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}
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return 0;
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}
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