递归调用（为什么会StackOverflowError）——八皇后算法
为什么我的这个算法有时会StackOverflowError，代码如下
package algorithm;public class EightQueen {/** * @param args */public static void main(String[] args) {EightQueen self = new EightQueen();for(int i=12;i<13;i++){self.queen(i);}}public void queen(int n){System.out.println("======== "+n+" ========");int[][] grid = new int[n][n];for(int i=0;i<n;i++){for(int j=0;j<n;j++){grid[i][j] = 0;}}init(grid,0,0,false,n);for(int i=0;i<n;i++){for(int j=0;j<n;j++){if(grid[i][j]==1){System.out.print(" + ");}else{System.out.print(" - ");}}System.out.println();}}public void init(int[][] grid,int horizontal,int vertical,boolean isBack,int size){if(isBack){if(horizontal==28&&vertical==16){System.out.println();}grid[horizontal][vertical] = 0;vertical++;}if(vertical>=size){horizontal--;if(horizontal<0){System.out.println("No result!");return ;}for(int i=0;i<size;i++){if(grid[horizontal][i]==1){init(grid,horizontal,i,true,size);return ;}}}for(int i=0;i<horizontal;i++){for(int j=0;j<size;j++){if(grid[i][j]==1&&!isFree(horizontal,vertical,i,j)){init(grid,horizontal,vertical,true,size);return ;}}}grid[horizontal][vertical] = 1;System.out.println(horizontal+":"+vertical);if(++horizontal>=size){return ;}init(grid,horizontal,0,false,size);return ;}private boolean isFree(int x,int y,int holdX,int holdY){if(x==holdX||y==holdY){//同一横排或竖排return false;}int slant1 = (x-holdX)-(y-holdY);int slant2 = (x-holdX)+(y-holdY);if(slant1==0||slant2==0){//两条斜线return false;}return true;}}package algorithm;public class Queen_Java {int QUEEN_COUNT = 20; // 是多少皇后static final int EMPTY = 0;int[][] count = new int[QUEEN_COUNT][QUEEN_COUNT];int[] QueenIndex = new int[QUEEN_COUNT];int resultCount = 0;long time = System.currentTimeMillis();public void putQueenIndex(int row) {for (int col = 0; col < QUEEN_COUNT; col++) {if (count[row][col] == EMPTY) {for (int iRow = row + 1; iRow < QUEEN_COUNT; iRow++) {count[iRow][col]++;if ((col - iRow + row) >= 0) {count[iRow][col - iRow + row]++;}if ((col + iRow - row) < QUEEN_COUNT) {count[iRow][col + iRow - row]++;}}QueenIndex[row] = col;if (row == QUEEN_COUNT - 1) {print(++resultCount);} else {putQueenIndex(row + 1);}for (int iRow = row + 1; iRow < QUEEN_COUNT; iRow++) {count[iRow][col]--;if ((col - iRow + row) >= 0) {count[iRow][col - iRow + row]--;}if ((col + iRow - row) < QUEEN_COUNT) {count[iRow][col + iRow - row]--;}}}}if (row == 0) {System.out.println(QUEEN_COUNT + "皇后共有 " + resultCount + " 个解\n"+ (System.currentTimeMillis() - time) + "毫秒");}}public void print(int n) {System.out.println(QUEEN_COUNT + "皇后的第 " + n + " 个解：");for (int i = 0; i < QUEEN_COUNT; i++) {for (int j = 0; j < QUEEN_COUNT; j++) {System.out.print(QueenIndex[i] == j ? " * " : " - ");}System.out.println();}System.out.println();}public static void main(String[] args) {new Queen_Java().putQueenIndex(0);}}