Tree Array - Array Operations (nkoj1321)

Tree arrays - array operations ( nkoj1321 )

topic analysis

tree array bare question

tree array

lowbit:i & -i

Since -i is expressed in complement, that is, each bit is inverted +1, so it i & -irepresents the value represented by the last 1 of i, such as lowbit(8)=8, lowbit(12)=4

operate

• newvoid build();

Record a prefix sum array ps, and then according to the nature of the tree array, s[i]=ps[i] - ps[i - (i & -i)], s[i] can be understood as the sum within the jurisdiction of i

• Revisevoid add(int pos, int delta);

i starts from pos and increases lowbit(i) each time, so that delta is added to all s[i] containing pos

• sumint sum(int pos);

i starts from pos and subtracts lowbit(i) each time, so that s[i] is the sum of each segment, and adding them all together is the prefix sum

code

//
// Created by rv on 2018/4/22.
//

#include <cstring>
#include <cstdio>

const int N = 100000 + 5;

// 注意下标一定不能从0开始
int A[N], ps[N];
int s[N];

void build() {
    for (int i = 1; i <= N; i++) {
        ps[i] = ps[i - 1] + A[i];
        s[i] = ps[i] - ps[i - (i & -i)];
    }
}

// 第pos个数加delta
void add(int pos, int delta) {
    for (int i = pos; i <= N; i += i & -i) {
        s[i] += delta;
    }
}

// 前pos个数的和
int sum(int pos) {
    int res = 0;
    for (int i = pos; i >= 1; i -= i & -i) {
        res += s[i];
    }
//    printf("sum: %d %d\n", pos, res);
    return res;
}

// [l,r]区间和
int ask(int l, int r) {
//    printf("ask: %d %d\n", l, r);
    return sum(r) - sum(l - 1);
}

int main() {
//    freopen("data.in", "r", stdin);
    int n, m, x, y, tmp;
    char str[4];
    char SUM[] = "SUM";
    char ADD[] = "ADD";
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) {
        scanf("%d", &A[i]);
//        scanf("%d", &tmp);
//        add(i, tmp);
    }
//    for (int i = 1; i <= n; i++) {
//        printf("%d ", A[i]);
//    }
//    printf("\n");
    build();
//    for (int i = 1; i <= n; i++) {
//        printf("%d ", ps[i]);
//    }
//    printf("\n");
//    for (int i = 1; i <= n; i++) {
//        printf("%d ", s[i]);
//    }
//    printf("\n");
    scanf("%d", &m);
    while (m--) {
        scanf("%s%d%d", str, &x, &y);
//        printf("str: %s\n", str);
        if (strcmp(str, SUM) == 0) {
//            printf("sum: ");
            printf("%d\n", ask(x, y));
        } else if (strcmp(str, ADD) == 0) {
//            printf("add: ");
            add(x, y);
        } else {
            printf("bad scanf");
        }
    }

    return 0;
}

pit

The return of strcmp is equal to 0, and it was reversed at the beginning and adjusted for a while...