[线段树] HDU 1698

一步一步理解线段树： http://www.cnblogs.com/TenosDoIt/p/3453089.html#f

还是这个地址，这次用到了优化所用的区间延迟更新，时间复杂度是O(lgn)

PS：领教到了不好好命名变量的坑爹之处。。。。。。。

#include 
#include 
#include 

#define lson root * 2
#define rson root * 2 + 1

using namespace std;
const int X = 100002 << 2;

int Tree[ X ];
int flag[ X ]; //延迟标记

void build ( int root, int ST, int END ) {
        if ( ST == END ) {
                Tree[ root ] = 1;
                flag[ root ] = 0;
        } else {
                int mid = ( ST + END ) / 2;
                build ( lson, ST, mid );
                build ( rson, mid + 1, END );
                Tree[ root ] = Tree[ lson ] + Tree[ rson ];
        }
}

// 延迟更新 时间O(lgn)
// 当前root的标记向下更新
void pushDown ( int root, int st, int end ) {
        if ( flag[ root ] ) {
                flag[ lson ] = flag[ rson ] = flag[ root ]; //传递z（要修改成）的值给子节点
                int mid = ( st + end ) / 2;
                Tree[ lson ] =
                    ( mid - st + 1 ) * flag[ root ]; //根代表的和 直接等于这段区间大小 * z
                Tree[ rson ] = ( end - ( mid + 1 ) + 1 ) * flag[ root ];
                flag[ root ] = 0;
        }
}

// ST END --> required
// st,end --> now
void update ( int root, int st, int end, int ST, int END, int val ) {
        if ( st > END || end < ST )
                return;

        //找到要更新的整段区间
        if ( st >= ST && end <= END ) {
                flag[ root ] = val;
                Tree[ root ] = val * ( end - st + 1 ); //更新这一段的根节点总和
                return;
        }

        //建立flag，延迟更新子节点
        pushDown ( root, st, end );

        int mid = ( st + end ) / 2;
        if ( mid >= ST )
                update ( lson, st, mid, ST, END, val );
        if ( mid < END )
                update ( rson, mid + 1, end, ST, END, val );

        Tree[ root ] = Tree[ lson ] + Tree[ rson ];
}

int main () {
        int n;
        scanf ( "%d", &n );
        for ( int i = 1; i <= n; ++i ) {

                memset ( flag, 0, sizeof ( flag ) );

                int N, Q;
                scanf ( "%d%d", &N, &Q );

                build ( 1, 1, N );

                while ( Q-- ) {
                        int x, y, z;
                        scanf ( "%d%d%d", &x, &y, &z );
                        update ( 1, 1, N, x, y, z );
                }

                printf ( "Case %d: The total value of the hook is %d.\n", i, Tree[ 1 ] );
        }

        return 0;
}