hdu 1394 线段树版~~~@ ！@

#include<stdio.h>#define N 5005struct node{ int l;int r;int sum;};int arr[N];node tree[3*N];void buid_tree(int k,int left,int right){int mid;int L,R;tree[k].l = left; tree[k].r = right;if(right-left == 1){tree[k].sum = 0;return ;}L = 2*k; R = L+1;mid = (left+right)/2;buid_tree(L,left,mid);buid_tree(R,mid,right);tree[k].sum = tree[L].sum+tree[R].sum;return ;}int tree_search(int k,int left,int right){int mid;int L,R;int ls = 0,rs = 0;if(left <= tree[k].l && right >= tree[k].r){ return tree[k].sum;}L = 2*k; R = L+1;mid = (tree[k].l+tree[k].r)/2;if(left < mid) ls = tree_search(L,left,right);if(right > mid) rs = tree_search(R,left,right);return ls+rs;}void tree_insert(int k,int left,int right){int mid;int L,R;if(left <= tree[k].l && right >= tree[k].r){ tree[k].sum += 1; return ;}L = 2*k; R = L+1;mid = (tree[k].l+tree[k].r)/2;if(left < mid) tree_insert(L,left,right);if(right > mid) tree_insert(R,left,right);tree[k].sum = tree[L].sum+tree[R].sum;return ;}int main(){int i;int m;int n;int flag;int count;int min;while(scanf("%d",&n) == 1){count = 0;buid_tree(1,0,N+1); for(i = 1;i <= n;i++){ scanf("%d",&arr[i]);count += i-1-tree_search(1,0,arr[i]);tree_insert(1,arr[i],arr[i]+1);}min = count;for(m = 1;m <= n-1;m++){flag = tree_search(1,0,arr[m]);count = count-flag+(n-1-flag);//之前太暴力了，每个序列都建一次树求出逆序数，果断超时了，后来百度了一下，才想到了这样，if(count < min) //每移动一个，逆序数 = 前面一个逆序数-所有数中比其小的数+所有数中比其大的数;min = count;}printf("%d/n",min);}return 0;}