HDU 1166 (segment tree)

An easy problem aiming at practicing the implementation of the segment tree. Apparently, we should use segment tree to solve it. And within the tree structure is the sum.

Note that the number of the nodes is much larger than the size of the integer array because of the "tree" structure. Otherwise, it may cause Runtime Error (ACCESS_VIOLATION).

AC Code:

#include <iostream>#include <cstdio>#include <cstring>#define INF 0x3f3f3f3f#define N 50010#define MST(a,b) memset(a,b,sizeof(a))#define FOR(i,a,b) for(int i=a;i<=b;i++)using namespace std;struct TREE {    int left,right;    int suml;} tree[900000];//*** Large Enough? ***void Built(int root,int l,int r){    tree[root].left = l;    tree[root].right = r;    tree[root].suml=0;    if(l == r)return;    int mid = (l+r) >> 1;    Built ( root<<1   , l , mid );    Built ( root<<1|1 , 1+mid , r);}void Fix(int root,int left,int right,int del) {    if (left == tree[root].left && tree[root].right == right) {        tree[root].suml += del;        return;    }    if (left < tree[root].left || right > tree[root].right)        return;    Fix(root << 1, left, right, del);    Fix(root << 1 | 1, left, right, del);    tree[root].suml += del;}int Query_sum(int root,int left,int right) {    if (left == tree[root].left && tree[root].right == right)        return tree[root].suml;    if (tree[root << 1 | 1].left > right)//left only        return Query_sum(root << 1, left, right);    if (left > tree[root << 1].right)//right only        return Query_sum(root << 1 | 1, left, right);    int s1 = 0, s2 = 0;    s1 = Query_sum(root << 1, left, tree[root << 1].right);    s2 = Query_sum(root << 1 | 1, tree[root << 1 | 1].left, right);    return s1 + s2;     if (left < tree[root].left || right > tree[root].right)        return -INF;}int main(){    int t,n,a,b;    cin>>t;    FOR(ncase,1,t) {        printf("Case %d:\n", ncase);        cin >> n;        Built(1, 1, n);        FOR(i, 1, n) {            cin >> a;            Fix(1, i, i, a);        }        char s[10];        cin >> s;        while (s[0] != 'E') {            cin >> a >> b;            if (s[0] == 'A') {                Fix(1, a, a, b);            }            else if (s[0] == 'S') {                Fix(1, a, a, -b);            }            else                printf("%d\n", Query_sum(1, a, b));            cin>>s;        }    }    return 0;}