OJ练习

1、京东OJ 保卫方案 （单调栈）

http://www.cnblogs.com/mengmz/p/7263915.html

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
struct node{
    int val;
    long count;
    node(int v, int c = 1): val(v), count(c){}
};

int main() {
    int N;
    while(cin >> N){
        vector<int> watch(N);
        for(int i = 0; i < N; ++i)
            cin >> watch[i];

        vector<node> v;
        node tmp(watch[0]);

        int max_h = watch[0];
        int max_index = 0;
        for(int i = 1; i < N; ++i){
            if(watch[i] == watch[i - 1])
                tmp.count ++;
            else{
                v.push_back(tmp);
                if( max_h < tmp.val){
                    max_h = tmp.val;
                    max_index = v.size() - 1;
                }
                tmp.val = watch[i];
                tmp.count = 1;
            }
        }
        // 最后一个元素
        v.push_back(tmp);
        if( max_h < tmp.val){
            max_h = tmp.val;
            max_index = v.size() - 1;
        }
        int n = 0;
        long count = 0;
        vector<node> stack;
        for(int i = max_index; n < v.size(); ++n, i = (i+1)%v.size()){
            while( stack.size() && v[i].val > stack[stack.size() - 1].val){
                node & tmp = stack[stack.size() - 1];
                count += 2 * tmp.count + tmp.count*(tmp.count - 1)/2;
                stack.pop_back();
            }

            if( stack.size()){
                if(v[i].val == stack[stack.size() - 1].val)
                    stack[stack.size() - 1].count += v[i].count;
                else
                    stack.push_back(v[i]);
            } else
                stack.push_back(v[i]);
        }
        while(stack.size()){
            node & tmp = stack[stack.size() - 1];
            count += tmp.count*(tmp.count - 1)/2;
            stack.pop_back();
            if(stack.size()) count += 2 * tmp.count;
            if(stack.size()==1 &&stack[stack.size()-1].count==1) count-=tmp.count;
        }
        cout << count<<endl;
    }
    return 0;
}

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