模板汇总——笛卡尔树

笛卡尔树

O(n)建立一颗该节点是当前子树的最值的二叉树.

代码:

void Build(){
    int n;
    scanf("%d", &n);
    for(int i = 1; i <= n; ++i) scanf("%d", &a[i]), L[i] = R[i] = 0;
    top = 0;
    for(int i = 1; i <= n; ++i){
        while(top && a[sta[top]] > a[i]) L[i] = sta[top--];
        if(top)  R[sta[top]] = i;
        sta[++top] = i;
    }
}