Language: C++

#include <cstdio>
#include <cassert>
#include <cstring>
#include <cmath>
#include <vector>
#include <algorithm>
using namespace std;

typedef long long int64;
#define pb push_back
#define mp make_pair
#define fs first
#define sc second
#define sz(a) ((int) (a).size())

const int N = 1111;
int n, m, a, b;
char res[N][N], tmp[N][N];
bool swapped;

void vert(int x, int y) {
	assert(res[x][y] == 0);
	assert((x >= 0) && (x + 1 < n));
	assert((y >= 0) && (y < m));
	res[x][y] = '^';
	res[x + 1][y] = 'v';		
}

void hor(int x, int y) {
	assert(res[x][y] == 0);
	assert((x >= 0) && (x < n));
	assert((y >= 0) && (y + 1 < m));
	res[x][y] = '<';
	res[x][y + 1] = '>';		
}

char change(char c) {
	if (c == '^') {
		return '<';
	}
	if (c == '<') {
		return '^';
	}
	if (c == 'v') {
		return '>';
	}
	if (c == '>') {
		return 'v';
	}
	return c;
}

bool go(int n, int m, int a, int b) {
	memset(res, 0, sizeof(res));
	int x = 0, y = 0;
   	while (true) {
   		if (x + 2 > n) {
   			x = 0;
   			y += 2;
   		}
   		if (y >= m) {
   			break;
   		}
   		if (b > 0) {
   			vert(x, y);
   			b--;
   		}
   		if ((b > 0) && (y + 1 < m)) {
   			vert(x, y + 1);
   			b--;
   		}
   		if (b == 0) {
   			break;
   		}
   		x += 2;
   	}
   	for (int i = 0; i < n; ++i) {
   		for (int j = 0; j + 1 < m; ++j) {
   			if ((a > 0) && (res[i][j] == 0)) {
   				hor(i, j);
   				--a;
   			}
   		}
   	}
   	return ((a == 0) && (b == 0));
}

bool greedy(int n, int m, int a, int b) {
	memset(res, 0, sizeof(res));
	for (int i = 0; i + 1 < n; ++i) {
		for (int j = 0; j < m; ++j) {
			if ((b > 0) && (res[i][j] == 0) && (res[i + 1][j] == 0)) {
				vert(i, j);
				b--;
			}
		}
	}
	for (int i = 0; i < n; ++i) {
		for (int j = 0; j + 1 < m; ++j) {
			if ((a > 0) && (res[i][j] == 0) && (res[i][j + 1] == 0)) {
				hor(i, j);
				a--;
			}
		}
	return ((a == 0) && (b == 0));
}

#define swap_all hello_it_is_me

void swap_all() {
	swapped = !swapped;
   	swap(n, m);
   	swap(a, b);
}

int main() {
	scanf("%d%d%d%d", &n, &m, &a, &b);
   	if (!go(n, m, a, b)) {
   		swap_all();
   		if (!go(n, m, a, b)) {
   			swap_all();
   			if (!greedy(n, m, a, b)) {
   				swap_all();
   				if (!greedy(n, m, a, b)) {
   					printf("NO\n");
   					return 0;
   				}
   			}
   		}
   	}
   	printf("YES\n");
   	if (swapped) {
   		for (int i = 0; i < n; ++i) {
   			for (int j = 0; j < m; ++j) {
   				tmp[j][i] = change(res[i][j]);
   			}
   		}
   		swap(n, m);
   		swap(tmp, res);
   	}
   	for (int i = 0; i < n; ++i) {
   		for (int j = 0; j < m; ++j) {
   			if (res[i][j] == 0) {
   				res[i][j] = '.';
   			}
   			printf("%c", res[i][j]);
   		}
   		printf("\n");
   	}
	return 0;
}

Compiler output:
a.cc: In function 'bool greedy(int, int, int, int)':
a.cc:110:17: error: a function-definition is not allowed here before '{' token
  110 | void swap_all() {
      |                 ^
a.cc:116:9: warning: empty parentheses were disambiguated as a function declaration [-Wvexing-parse]
  116 | int main() {
      |         ^~
a.cc:116:9: note: remove parentheses to default-initialize a variable
  116 | int main() {
      |         ^~
      |         --
a.cc:116:9: note: or replace parentheses with braces to value-initialize a variable
a.cc:116:12: error: a function-definition is not allowed here before '{' token
  116 | int main() {
      |            ^
a.cc:151:2: error: expected '}' at end of input
  151 | }
      |  ^
a.cc:88:41: note: to match this '{'
   88 | bool greedy(int n, int m, int a, int b) {
      |                                         ^
a.cc:151:2: warning: control reaches end of non-void function [-Wreturn-type]
  151 | }
      |  ^