Google Code Jam 2015 * Qualification Round * Problem A. Standing Ovation

A.go

/*
*  Google Code Jam
*  2015 Qualification Round
*  Problem A. Standing Ovation
*  AQ <aq@okaq.com>
 */
package main

import (
	"bufio"
	"fmt"
	"os"
	"strconv"
	"strings"
	"sync"
	"time"
)

const (
	IN  = "A-large-practice.in"
	OUT = "A-large-practice.out"
)

var (
	I  *os.File
	O  *os.File
	S  *bufio.Scanner
	W  *bufio.Writer
	T  int
	Op []*Opera
	WG sync.WaitGroup
)

type Opera struct {
	Max int
	Shy []int
	Sum []int
	F   int
}

func NewOpera() *Opera {
	return &Opera{}
}

func (o *Opera) Solve() {
	o.F = 0
	o.Sum[0] = o.Shy[0]
	for i := 1; i < o.Max+1; i++ {
		// o.Sum[i] = o.Sum[i-1] + o.Shy[i] // take diff
		if o.Sum[i-1] < i {
			d := i - o.Sum[i-1]
			o.F = o.F + d
			o.Sum[i] = o.Sum[i-1] + o.Shy[i] + d
		} else {
			o.Sum[i] = o.Sum[i-1] + o.Shy[i]
		}
	}
	// fmt.Println(o)
	WG.Done()
}

func Load() {
	var err error
	I, err = os.Open(IN)
	if err != nil {
		fmt.Println(err)
	}
	S = bufio.NewScanner(I)
	O, err = os.Create(OUT)
	if err != nil {
		fmt.Println(err)
	}
	W = bufio.NewWriter(O)
}

func Cases() {
	var err error
	S.Scan()
	T, err = strconv.Atoi(S.Text())
	if err != nil {
		fmt.Println(err)
	}
	fmt.Printf("%d test cases. \n", T)
}

func Split() {
	var err error
	Op = make([]*Opera, T)
	for i := 0; i < T; i++ {
		o := NewOpera()
		S.Scan()
		a := strings.Split(S.Text(), " ")
		// fmt.Println(a)
		o.Max, err = strconv.Atoi(a[0])
		if err != nil {
			fmt.Println(err)
		}
		o.Shy, err = Levels(a[1])
		if err != nil {
			fmt.Println(err)
		}
		o.Sum = make([]int, o.Max+1)
		// fmt.Println(o)
		Op[i] = o
		WG.Add(1)
		go Op[i].Solve()
	}
}

func Levels(s string) ([]int, error) {
	var err error
	r := make([]int, len(s))
	// for i, e := range s { // range decodes the rune
	for i := 0; i < len(s); i++ {
		s0 := string(s[i])
		r[i], err = strconv.Atoi(s0)
		if err != nil {
			return r, err
		}
	}
	return r, err
}

func Finish() {
	defer I.Close()
	defer O.Close()
	for i := 0; i < T; i++ {
		s0 := fmt.Sprintf("Case #%d: %d\n", i+1, Op[i].F)
		W.WriteString(s0)
	}
	W.Flush()
}

func main() {
	begin := time.Now()
	Load()
	Cases()
	Split()
	WG.Wait()
	Finish()
	end := time.Now()
	fmt.Printf("total running time: %v. \n", end.Sub(begin))
}

// linear solution using sum array
// total run time: 16ms for large set