PAT 1007

前缀和

#include <bits/stdc++.h>
using namespace std;
const int maxn = 10010;

int num[maxn], pre[maxn] = {0};
int ext[maxn] = {0};

int main()
{
    int n; scanf("%d", &n);
    int cnt = 0;
    for(int i = 1; i <= n; i++){
        scanf("%d", &num[i]);
        if(i == 0) pre[i] = num[i];
        else pre[i] = pre[i-1] + num[i];
        if(num[i] < 0) cnt++;
    }
    int Min = 1<<30;
    for(int i = 0; i <= n; i++){
        if(pre[i] < Min){
            Min = pre[i];
            ext[i] = i;
        }else{
            ext[i] = ext[i-1];
        }
    }
    int Max = -1e9, l, r;
    for(int i = 1; i <= n; i++){
        if(pre[i]-pre[ext[i]] > Max){
            Max = pre[i]-pre[ext[i]];
            l = ext[i]+1, r = i;
        }
    }
    if(cnt == n){
        printf("0 %d %d\n", num[1], num[n]);
        return 0;
    }
    if(l < r)
        printf("%d %d %d\n", Max, num[l], num[r]);
    else
        printf("%d %d %d\n", num[l], num[l], num[l]);
    return 0;
}

DP

#include <bits/stdc++.h>
using namespace std;
const int maxn = 10010;

int num[maxn] = {0}, dp[maxn] = {0}, pos[maxn] = {0};

int main()
{
    int cnt = 0;
    int n; scanf("%d", &n);
    for(int i = 1; i <= n; i++){
        scanf("%d", &num[i]);
        if(num[i] < 0) cnt++;
    }
    for(int i = 1; i <= n; i++){
        if(dp[i-1] <= 0){
            dp[i] = num[i];
            pos[i] = i;
        }else{
            dp[i] = dp[i-1] + num[i];
            pos[i] = pos[i-1];
        }
    }
    int Max = -1e9, l, r;
    for(int i = 1; i <= n; i++){
        if(dp[i] > Max){
            Max = dp[i];
            l = pos[i], r = i;
        }
    }
    if(cnt == n) printf("0 %d %d\n", num[1], num[n]);
    else printf("%d %d %d\n", Max, num[l], num[r]);
    return 0;
}