HDU2553 N Queen Question

Problem Link: HDU2553 n queen problem. Basic Training questions, written in C language program.

Originally did solve the problem of the N queen of the procedure, it is easy to rewrite a bit. For procedures, see: Eight Queens (n Queens) problem algorithm program.

One submission, "Time Limit exceeded", had to hit the table first. The original code comment was left there.

This is a classic backtracking procedure, is to use the recursive return to achieve, in fact, can also be implemented with non-recursive return. Backtracking does not have to be done with recursion.

The details of the program still need to be noted, such as when playing a table, you need to declare more than one element, because the array subscript is starting from 0.

The AC program is as follows:

/* HDU2553 N Queen Problem */#include <stdio.h> #define TRUE 1#define FALSE 0#define maxqueen 10#define ABS (x) ((x>0)? (  x):-(x)//* For the absolute value of x *//* Store 8 Queens of the column position, the array is labeled as the Queen's column position */int Queen[maxqueen];int total_solution;    /* Calculates a total of several sets of solutions *//* test whether the Queen on (Row,col) is under attack and returns a value of 1 if attacked, otherwise returns 0 */int attack (int row, int col) {int i, atk=false;    int Offset_row, Offset_col;    i=0;        while (!atk && i<row) {offset_row=abs (i-row);        Offset_col=abs (Queen[i]-col); /* Determine if the two queens are in the same column, whether on the same diagonal *//* If the two queens are in the same column or diagonal, then the attack occurs, atk==true */ATK = (queen[i] = = col) | |        (Offset_row = = Offset_col);    i++; } return ATK;}    /* Recursive placement of Queen subroutine */void place (int q, int n) {int i=0;             while (I < n) {if (!attack (q, i))/*/Queen not attacked */{queen[q]=i;   /* Store Queen's column position */* To determine if a set of solutions */if (q = = n-1) total_solution++;      /* Get a solution */else place (q+1, n); /* Otherwise continue to put the next Queen */} i++;   }}int Main (void) {int n;    int ans[maxqueen+1], I;        Because "time Limit exceeded", had to first hit the table for (i=1; i<=maxqueen; i++) {//Queen traversal total_solution = 0;                Place (0, I);    /* Starting from the No. 0 queen to the board */ans[i] = total_solution;        } while (scanf ("%d", &n)! = EOF) {//Judgment end Condition if (n = = 0) break;                Queen Traversal//total_solution = 0;//Place (0, N);        /* Starting from the No. 0 queen to the board *///output//printf ("%d\n", total_solution);    printf ("%d\n", Ans[n]); } return 0;}

HDU2553 N Queen Question