Poj #1011-sticks

This is really classic searching problem to solve. The key is pruning.

(My reference: http://blog.csdn.net/lyy289065406/article/details/6647960)

There are total 4 pruning strategies to take:

1. The target length is between Max section length to total length-piece of cake
2. The target length shocould: totallength % targetlength = 0-piece of cake
3. Since there cocould be duplicated seece, if one of them doesn't work, all other sections with the same length can be skipped-piece of cake
4. At the beginning of a new search, if it doesn't work, we can simply skip all other following sticks-It made TLE to AC as 16 Ms

And yes I'm a rookie and I learned it by retyping:

//    1011//    http://blog.csdn.net/lyy289065406/article/details/6647960#include <stdio.h>#include <stdlib.h>#include <algorithm> using namespace std;#define MAX_STICK 64bool cmp (int i,int j) { return (i > j); }bool dfs(int *sticks, bool *visited, int currLen, int tgtLen, int currInx, int usedCnt, int n){    if(usedCnt == n) return true;    int skipLen = -1;    for(int i = currInx; i < n; i ++ )    {        if(visited[i] || sticks[i] == skipLen) continue;    // Pruning 3: if that len needs to be skipped                visited[i] = true;        int currCmb = currLen + sticks[i];        if(currCmb < tgtLen)        {            if(dfs(sticks, visited, currCmb, tgtLen, i, usedCnt + 1, n))                return true;            else                skipLen = sticks[i];         }        else if(currCmb == tgtLen)        {            if(dfs(sticks, visited, 0, tgtLen, 0, usedCnt + 1, n))                return true;            else                skipLen = sticks[i];         }        visited[i] = false;                    if(currLen == 0) break;    // Pruning 4: for starting point 0, no matches then NO                                // * it makes TLE passing as 16MS    }    return false;}int main(){    int n;     while (scanf("%d", &n), n != 0)    {        int sticks[MAX_STICK] = { 0 };        bool visited[MAX_STICK]    = { false };        //    Input        int sum = 0;        for(int i = 0; i < n; i ++)         {            scanf("%d", sticks + i);            sum += sticks[i];        }        //    Sort descending        sort (sticks, sticks + n, cmp);        //    Searching by pruning        bool bFound = false;        for(int l = sticks[0]; l <= sum - l; l ++)    //    Pruning 1        {            if( (sum % l == 0) && dfs(sticks, visited, 0, l, 0, 0, n))    // Pruning 2            {                bFound = true;                printf("%d\n", l);                break;            }        }        if(!bFound)    printf("%d\n", sum);            }    return 0;}

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